bluuebunny/crossref_metadata_2025 huggingface dataset:
Tree growth response to the 1913 eruption of Volcán de Fuego de Colima, Mexico
Authors: Biondi Franco , Estrada Ignacio Galindo , Gavilanes Ruiz Juan Carlos , Torres Alejandro Elizalde
Published: May 2003

The impact of volcanic eruptions on forest ecosystems can be investigated using dendrochronological records. While long-range effects are usually mediated by decreased air temperatures, resulting in frost rings or reduced maximum latewood density, local effects include abrupt suppression of radial growth, occasionally followed by greater than normal growth rates. Annual rings in Mexican mountain pine (Pinus hartwegiiLindl.) on Nevado de Colima, at the western end of the Mexican Neovolcanic Belt, indicate extremely low growth in 1913 and 1914, following the January 1913 Plinian eruption of Volcán de Fuego, 7.7 km to the south. That event, which is listed among the largest explosive eruptions since A.D. 1500, produced ashflow deposits up to 40 m thick and blanketed our study area on Nevado de Colima with a tephra fallout 15–30 cm deep. Radial growth reduction in 1913–14 was ≥30% in 73% of the sampled trees. We geostatistically investigated the ecological impact of the eruption by mapping the decrease in xylem increment and found no evidence of a spatial structure in growth reduction. Little information has been available to date on forest species as biological archives of past environments in the North American tropics, yet this historical case study suggests that treeline tropical sites hold valuable records of prehistoric phenomena, including volcanic eruptions.
Restorative potential of cholinergic rich transplants in cholchicine induced lesioned rats: a comparative study of single and multiple micro‐transplantation approach
Authors: Agrawal A.K. , Roy Adip , Seth K. , Raghubir Ram , Seth P.K.
Published: May 2003

Restorative potential of fetal neural transplantation in colchicine induced neurodegeneration was studied in rats; where colchicine (2.5 mg per site) was administered bilaterally into the hippocampus followed by bilateral infusions of fetal neural cell suspension rich in cholinergic neurons as single macro‐ or multiple micro‐transplants in the hippocampal region 3 weeks post‐colchicine (2.5 mg per site) lesion. Animals were studied for neuro behavioural and neurochemical recovery at 4 and 24 weeks post‐transplantation and electrophysiological (single cell recording) and immunohistochemical parameters, choline acetyl transferase (ChAT) expression was studied in hippocampus at 24 weeks post‐transplantation. Colchicine lesioned rats receiving single macro‐ or multiple micro‐transplants exhibited significant restoration in cognitive dysfunction caused by colchicine after 4 weeks of transplantation which remain persistent in multiple micro‐transplanted group upto 24 weeks post‐transplantation, whereas, single macro‐transplanted animals did not exhibit any significant recovery. Neurochemical studies revealed significant restoration in acetylcholine esterase activity and cholinergic (muscarinic) receptor binding after 24 weeks post‐transplantation as compared to 4 weeks post‐transplantation in multiple micro‐transplanted group. Single cell recording studied at 24 weeks post‐transplantation exhibited significant restoration in firing rates when compared with lesioned group. The viability of cholinergic fibre at transplanted sites has further been confirmed by increase in ChAT immuno positivity in hippocampal region using monoclonal antibody and quantified using image analyser Leica Qwin 500 software. The results suggest that intra‐hippocampal multiple site cholinergic rich transplants provide better and long term restoration in the cholinergic deficits induced by colchicine lesion as compared to single site macro‐transplantation.
Late onset alcoholism
Authors: Wetterling Tilman , Veltrup Clemens , John Ulrich , Driessen Martin
Published: May 2003

Rather high prevalence rates of alcohol abuse in the elderly have been reported in the literature. However, there is some evidence that many elderly persons with alcohol problems are not identified, probably due to the nonspecificity of alcohol-related presentations in old individuals. Thus, there is an ongoing discussion on appropriate diagnostic criteria for alcohol dependence in elder people who frequently begin to abuse alcohol in late life. This study was aimed to explore whether alcoholics with late onset (beginning after the age of 45) differ from those with an early onset (prior the age of 25). Two hundred and sixty eight subjects consecutively referred to a ward of a general hospital specialized for alcohol detoxification were divided into three groups by the age at onset of harmful alcohol consumption. The duration of harmful drinking was rather similar in all groups. However, alcohol dependence according to the ICD-10 criteria (three or more have to be fulfilled) was diagnosed in 94.1% of the alcoholics with an early onset (≤ 25 years), but only in 62.2% of those with late onset (P < 0.0001). Significant differences between these groups were found for the following criteria: preoccupation with drinking (P < 0.0001), impaired capacity to control drinking (P < 0.01), strong desire to drink alcohol (P < 0.01), and a trend towards a lower rate of lifetime psychiatric comorbidity. The alcoholics with late onset reported fewer previous detoxifications and a lower actual alcohol consumption. Moreover, they showed a higher rate of abstinence in the 12 month follow-up. Regarding the difficulties in comparing groups of different ages at onset of harmful alcohol use our results suggest that the alcoholics with late onset differ in many ways from those with early onset.
The first-episode of schizophrenia: a challenge for treatment
Authors: Fleischhacker W.W.
Published: May 2003

For young people experiencing a first-episode of schizophrenia, the first and most important matter to be attended to, once the diagnosis of schizophrenia has been made and patients have entered the care system, is to establish a treatment alliance. The next step is to conceive an individually tailored treatment programme (non-pharmacological as well as pharmacological). The use of antipsychotic drugs needs to be carefully discussed with both patients and families, as medication tends to have a poor public perception. Maintaining treatment is vitally important in terms of relapse prevention, but people who suffer a first-episode tend to terminate treatment early. Patients often discontinue their medication because of side-effects, although a number of other factors can also exert a negative influence on the continuous intake of medication. Among others, these include insufficient information provided to patients and significant others as well as lack of insight and problems in the doctor-patient-relationship. The published data indicate that the outcome of treatment is better for younger patients in a first-episode of schizophrenia than it is for patients who are more chronically ill. However, young patients are much more sensitive to compliance problems than older patients. The main challenge in this phase of the illness is therefore to convince patients that maintenance treatment is necessary in order to assure the best possible outcome.
Mycophenolate mofetil (MMF) for the treatment of steroid‐resistant idiopathic thrombocytopenic purpura
Authors: Hou Ming , Peng Jun , Shi Yan , Zhang Chunqing , Qin Ping , Zhao Chuanli , Ji Xuebin , Wang Xueyong , Zhang Maohong
Published: May 2003

Abstract: The treatment of chronic idiopathic thrombocytopenic purpura (ITP) is difficult in those unresponsive to corticosteroids and/or splenectomy. We attempted to induce durable response in 21 patients with refractory ITP by applying mycophenolate mofetil (MMF) (1.5–2.0 g/d), a novel immunosuppressive agent. Overall response rate was 62% (13 of 21), including 24% (five of 21) in complete response (CR), 29% (six of 21) in partial response (PR), and 10% (two of 21) in minor response (MR). The response rates for non‐splenectomized and splenectomized ITP patients were 64% (nine of 14) and 57% (four of seven), respectively (P > 0.05). 39% (five of 13) responders relapsed as a result of dose reduction or withdraw of MMF, and 61% (eight of 13) responders maintained their effectiveness for a median of 24 wk. Sustained response was observed in three patients in whom MMF was withdrawn. MMF was well tolerated with only slight nausea and diarrhea recorded in 3 of 21 cases. No premature withdrawal was found in this study. CD3+ peripheral blood mononuclear cells (PBMC) and CD19+ PBMC were significantly reduced 12 wk after MMF administration in the responders. Platelet‐associated antibodies against glycoproteins GPIIb/IIIa were detected in 13 of 21 (62%) patients before MMF treatment, and antibody levels were significantly decreased in responders 12 wk after MMF administration. This suggested that MMF might correct the immunologic abnormalities underlying the destruction of circulating platelets in ITP. We conclude that MMF could be used as a second‐line agent for the treatment of steroid‐resistant ITP before or after splenectomy and thereby is worth of further evaluation in randomized studies.
Stimulation of c‐MYC transcriptional activity and acetylation by recruitment of the cofactor CBP
Authors: Vervoorts Jörg , Lüscher‐Firzlaff Juliane M , Rottmann Sabine , Lilischkis Richard , Walsemann Gesa , Dohmann Karen , Austen Matthias , Lüscher Bernhard
Published: May 2003

The c‐MYC oncoprotein regulates various aspects of cell behaviour by modulating gene expression. Here, we report the identification of the cAMP‐response‐element‐binding protein (CBP) as a novel c‐MYC binding partner. The two proteins interact both in vitro and in cells, and CBP binds to the carboxy‐terminal region of c‐MYC. Importantly, CBP, as well as p300, is associated with E‐box‐containing promoter regions of genes that are regulated by c‐MYC. Furthermore, c‐MYC and CBP/p300 function synergistically in the activation of reporter‐gene constructs. Thus, CBP and p300 function as positive cofactors for c‐MYC. In addition, c‐MYC is acetylated in cells. This modification does not require MYC box II, suggesting that it is independent of TRRAP complexes. Instead, CBP acetylates c‐MYC in vitro, and co‐expression of CBP with c‐MYC stimulates in vivo acetylation. Functionally, this results in a decrease in ubiquitination and stabilization of c‐MYC proteins. Thus, CBP and p300 are novel functional binding partners of c‐MYC.
A crucial role for profilin–actin in the intracellular motility of Listeria monocytogenes
Authors: Grenklo Staffan , Geese Marcus , Lindberg Uno , Wehland Jürgen , Karlsson Roger , Sechi Antonio S
Published: May 2003

We have examined the effect of covalently crosslinked profilin–actin (PxA), which closely matches the biochemical properties of ordinary profilin–actin and interferes with actin polymerization in vitro and in vivo, on Listeria monocytogenes motility. PxA caused a marked reduction in bacterial motility, which was accompanied by the detachment of bacterial tails. The effect of PxA was dependent on its binding to proline‐rich sequences, as shown by the inability of PH133S xA, which cannot interact with such sequences, to impair Listeria motility. PxA did not alter the motility of a Listeria mutant that is unable to recruit Ena (Enabled)/VASP (vasodilator‐stimulated phosphoprotein) proteins and profilin to its surface. Finally, PxA did not block the initiation of actin‐tail formation, indicating that profilin–actin is only required for the elongation of actin filaments at the bacterial surface. Our findings provide further evidence that profilin–actin is important for actin‐based processes, and show that it has a key function in Listeria motility.
Control of triglyceride storage by a WD40/TPR‐domain protein
Authors: Häder Thomas , Müller Sandra , Aguilera Miguel , Eulenberg Karsten G , Steuernagel Arnd , Ciossek Thomas , Kühnlein Ronald P , Lemaire Lydia , Fritsch Rüdiger , Dohrmann Cord , Vetter Ingrid R , Jäckle Herbert , Doane Winifred W , Brönner Günter
Published: May 2003

Obesity is a metabolic disorder related to improper control of energy uptake and expenditure, which results in excessive accumulation of body fat. Initial insights into the genetic pathways that regulate energy metabolism have been provided by a discrete number of obesity‐related genes that have been identified in mammals. Here, we report the identification of the adipose (adp) gene, the mutation of which causes obesity in Drosophila. Loss of adp activity promotes increased fat storage, which extends the lifespan of mutant flies under starvation conditions. By contrast, adp gain‐of‐function causes a specific reduction of the fat body in Drosophila. adp encodes an evolutionarily conserved WD40/tetratricopeptide‐repeat‐domain protein that is likely to represent an intermediate in a novel signalling pathway.
Adverse renal effects of anti‐inflammatory agents: evaluation of selective and nonselective cyclooxygenase inhibitors
Authors: Gambaro G. , Perazella M. A.
Published: May 2003

Abstract. Gambaro G, Perazella MA (Division of Nephrology, University Hospital, Padua, Italy; and Section of Nephrology, Yale University, New Haven, CT, USA). Adverse renal effects of anti‐inflammatory agents: evaluation of selective and nonselective cyclooxygenase inhibitors (Review). J Intern Med 2003; 253: 643–652.

Conventional nonsteroidal anti‐inflammatory drugs (NSAIDs), i.e. nonselective cyclooxygenase COX inhibitors have well‐documented nephrotoxicity. Adverse renal effects occur because of inhibition of the synthesis of cyclooxygenase‐derived prostaglandins which act to modulate pathologic processes that would normally impair various renal functions. The introduction of the selective COX‐2 inhibitors raised hope that this class of drugs would reduce injury in both the gastrointestinal tract and the kidneys. Animal and human data, however, suggest that COX‐2 synthesized prostaglandins are important in the modulation of renal physiology during adverse conditions. Hence, it appears that these drugs are equal in causing nephrotoxicity as the nonselective COX inhibitors.
The treatment of sporadic versus MEN1‐related pituitary adenomas
Authors: Beckers A. , Betea D. , Socin H. Valdes , Stevenaert A.
Published: May 2003

Abstract.  Beckers A, Betea D, Valdes Socin H, Stevenaert A (Domaine Universitaire du Sart‐Tilman, Liege, Belgium). The treatment of sporadic versus MEN1‐related pituitary adenomas (Minisymposium). J Intern Med 2003; 253: 599–605.

The treatment of pituitary tumours strongly depends on their clinical presentation. In general, the treatment aims are reducing tumour volume and/or decreasing hormone hypersecretion. It relies on single or a combination of three different methods: surgery, medication and radiotherapy. The rationale for deciding the treatment are many but include the aggressiveness of the tumour. The aetiologies of sporadic pituitary adenomas are not fully understood. However, several causes have been identified resulting in specific familial phenotypes like multiple endocrine neoplasia type I (MEN1). MEN1 is related to mutations in the MEN1 gene, a tumour suppressor gene localized on chromosome 11q13 and which encodes menin, a 610 amino acid protein. During the last years, an evidence progressively emerged that MEN1‐related adenomas were more aggressive and less responsive to therapy than their sporadic counterparts. In this article, we review the differences between sporadic and MEN1‐related adenomas and suggest specific ways of treatment and follow‐up for MEN1‐related tumours.
Long-term results of percutaneous management for anastomotic biliary stricture after orthotopic liver transplantation
Authors: Roumilhac Didier , Poyet Grégory , Sergent Géraldine , Declerck Nicole , Karoui Mehdi , Mathurin Phillippe , Ernst Olivier , Paris Jean-Claude , Gambiez Luc , Pruvot François-René
Published: May 2003

The purpose of this study was to evaluate the results of percutaneous transhepatic management (PTM) of anastomotic biliary strictures (BS). Among 168 liver transplant adult recipients, BS was identified in 30 patients. In 6 patients, narrowing of the anastomosis was found early, and in all cases disappeared spontaneously with prolonged draining of the bile tube. Within a mean time of 14 months after transplantation, 24 patients had symptomatic BSs, revealed by cholestasis (n = 17) or cholangitis (n = 7). Twenty-two patients underwent PTM as first treatment of BS (balloon dilatation or stent placement). We evaluated the primary and secondary patency rate of PTM. In 1 patient, PTM failed because the stricture could not be passed with the guide wire, necessitating conversion to a Roux-en-Y choledochojejunostomy (CDJ). Fourteen patients were treated by percutaneous balloon dilatation from which 8 patients (57.2%) were recurrence-free with a mean follow-up of 61 months. One patient with a patent biliary anastomosis underwent retransplantation for acute rejection. Twelve patients received metallic expandable stent placement as their primary treatment (n = 7) or after failure of balloon dilatation (n = 5). Recurrent stricture was found in 7 cases (58%) and was treated by PTM (n = 6) or surgery (n = 1). The primary patency rate for PTM was 58.8% at 12 months and the secondary patency rate 88.4%, with a mean follow-up of 47 months (median: 44 months). The mortality rate was 3.5% (one death). PTM with balloon dilatation, stent placement, or both, represent a safe method to treat anastomotic BSs after orthotopic liver transplantation (OLT) resulting in a secondary patency rate of 88% at 5 years.
Recombinant adeno-associated virus vector: Is it ideal for gene delivery in liver transplantation?
Authors: Yang Zhen-Fan , Wu Xiao-Bing , Tsui Tung-Yu , Hou Yun-De , Luk John M. , Fan Sheung-Tat
Published: May 2003

Recombinant adeno-associated virus vector (rAAV) is an effective and safe gene-delivery tool. However, its application in solid-organ transplantation has not been addressed. The present study is designed to introduce human cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin G (hCTLA4Ig) by rAAV (rAAV-hCTLA4Ig) into rat liver grafts to analyze the effects of virus titer, exposure time, and route of administration on transgene expression and possible side effects caused by the gene-delivery approach. Different rAAV-hCTLA4Ig titers were introduced into liver grafts through back-table portal vein perfusion and preserved for a certain time. rAAV-hCTLA4Ig also was administered by intravenous and intramuscular injection. Transgene expression in grafts and plasma was detected by immunohistochemistry and enzyme-linked immunosorbent assay. Intragraft cytokine level was detected by reverse-transcriptase polymerase chain reaction. Anti-hCTLA4Ig antibodies in plasma were detected by flow cytometry. A higher virus titer (1 × 1012 viral genomes/animal) introduced through back-table portal vein perfusion and a longer preservation time (3 hours) achieved a greater level of transgene expression until day 180. Back-table portal vein perfusion induced a greater level of hCTLA4 expression in plasma than intramuscular or intravenous injection. Increased interleukin-2 and interferon-γ messenger RNA levels were detected in grafts with rAAV-hCTLA4Ig gene transfer compared with those without virus delivery, but the response was minor. Such a cellular immune response could be suppressed by low-dose FK506 administration during the first 3 postoperative days. Anti-hCTLA4Ig antibodies could be detected in long-term surviving animals, but the extent of humoral response was not severe. This study shows that rAAV can be an effective and safe vector for gene delivery in liver transplantation.
MELD score predicts 1-year patient survival post-orthotopic liver transplantation
Authors: Saab Sammy , Wang Victor , Ibrahim Ayman B. , Durazo Francisco , Han Steven , Farmer Douglas G. , Yersiz Hasan , Morrisey Marcia , Goldstein Leonard I. , Ghobrial Mark R. , Busuttil Ronald W.
Published: May 2003

The Model for End-Stage Liver Disease (MELD) is an important predictor in patients awaiting orthotopic liver transplantation (OLT). However, the model’s association with posttransplant patient survival is unclear. We studied 1-year patient survival in 404 adult patients who underwent OLT at the University of California Los Angeles. The hazard rates of patient survival according to the MELD strata and United Network for Organ Sharing (UNOS) statuses were assessed by Proportional Hazard Cox regression analysis. The difference in survival for MELD strata and UNOS status were compared using the Cox model. There was a significant difference in 1-year patient (P = .0006) survival using different MELD strata, whereas there was a trend according to UNOS status (P = .051). Increased rate of death was observed in recipients of OLT with higher MELD scores (> 36, hazard ratio 3.9; 95% CI 1.55, 10.27) and more urgent UNOS status (2A; hazard ratio, 1.99; 95% CI 1.07, 3.7). The MELD stratum is better associated with 1-year patient survival in liver transplant recipients than UNOS statuses. Patient survival was worse with higher MELD scores.
Hepatic allograft-derived Kupffer cells regulate T cell response in rats
Authors: Sun Zhaoli , Wada Tatehiko , Maemura Kosei , Uchikura Keiichiro , Hoshino Sumito , Diehl Anna Mae , Klein Andrew S.
Published: May 2003

In liver transplantation, the development of tolerance is associated with an increased rate of apoptosis of T lymphocytes in the portal inflammatory infiltrate and the presence of an intragraft Th2-like T cell population. Underlying mechanisms are poorly understood. Kupffer cells (KC), which reside in the hepatic sinosoids, can directly interact with circulating T lymphocytes and thus are uniquely positioned to play a role in immunomodulation. In this study, the immunoregulatory effects of KC were investigated. We show that KC can significantly suppress T cell proliferation in mixed leukocyte reaction (MLR). Furthermore, KC express functional Fas ligand (FasL) and can induce apoptosis of Fas+ cells. This process can be blocked by addition of neutralizing anti-FasL antibody. Moreover, using an allogeneic liver transplant model we have determined that 1. KC recovered from chronically accepted hepatic allografts have increased FasL messenger RNA (mRNA) and protein expression and a greater ability to induce apoptosis of alloreactive T cells compared with KC recovered from an acute rejection model; 2. KC not only induce apoptosis of T cells, but also regulate cytokine production and Th2/Th3-like cytokine (interleukin [IL]-10 / transforming growth factor [TGF]-β) mRNA expression in allogeneic MLR in vitro; and 3. administration of KC derived from chronically accepted liver allografts significantly prolongs the survival of hepatic allografts in an acute rejection model in an alloantigen-specific manner. In conclusion, these data implicate the possible role of KC-mediated regulation of T cell response in the induction of immune tolerance in liver allografts
Design of a fast in situ infrared diagnostic tool
Authors: van Hest M. F. A. M. , Klaver A. , Schram D. C. , van de Sanden M. C. M.
Published: May 2003

Conventional Fourier transform infrared (FTIR) spectroscopes cannot be used to perform real time in situ infrared reflection absorption spectroscopy at monolayer sensitivity for high deposition rates (a couple of tens to hundreds of nm/s) which can be obtained when using an expanding thermal deposition plasma. Therefore a new analysis tool has been developed. The tool is based on a fast optical scanner in combination with conventional grating technology. This results in a loss of spectral range with respect to FTIR spectroscopes, but a significant gain is obtained in time resolution. For the combination used this makes it possible to measure at time resolution as low as 1.3 ms and resolution of 24 cm−1 at 1000 cm−1. The absorption sensitivity for single reflection at the best time resolution is approximately 10−2, but can be improved by using signal enhancement techniques. Here attenuated total reflection is used and the best sensitivity obtained is approximately 10−3, which is close to monolayer sensitivity for various absorption bands in the infrared spectrum of silicon oxide films. Monolayer sensitivity can be obtained by averaging multiple spectra, however this will cause the time resolution to decrease.
Noncontact atomic force microscopy: Stability criterion and dynamical responses of the shift of frequency and damping signal
Authors: Couturier G. , Boisgard R. , Nony L. , Aimé J. P.
Published: May 2003

The aim of this article is to provide a complete analysis of the behavior of a noncontact atomic force microscope (NC-AFM). We start with a review of the equations of motion of a tip interacting with a surface in which the stability conditions are first revisited for tapping mode. Adding the equations of automatic gain control (AGC), which insures constant amplitude of the oscillations in the NC-AFM, to the equations of motion of the tip, a new analytical stability criterion that involves proportional and integral gains of AGC is deduced. Stationary solutions for the shift of frequency and for the damping signal are obtained. Special attention is paid to the damping signal in order to clarify its physical origin. The theoretical results are then compared to those given by a virtual machine. The virtual machine is a set of equations solved numerically without any approximation. The virtual machine is of great help in understanding the dynamical behavior of the NC-AFM as images are recorded. Transient responses of the shift in frequency and of the damping signal are discussed in relation to the values of proportional and integral gains of AGC.
Application of carbon nanotubes to topographical resolution enhancement of tapered fiber scanning near field optical microscopy probes
Authors: Huntington S. T. , Jarvis S. P.
Published: May 2003

Scanning near field optical microscopy (SNOM) probes are typically tapered optical fibers with metallic coatings. The tip diameters are generally in excess of 300 nm and thus provide poor topographical resolution. Here we report on the attachment multiwalled carbon nanotubes to the probes in order to substantially enhance the topographical resolution, without adversely affecting the optical resolution.
Baseline resolution of 1,2H and 3,4He isotope mixtures with a Paul ion trap mass spectrometer
Authors: Orient O. J. , Chutjian A.
Published: May 2003

A Paul ion trap mass spectrometer with fractional resolution of m/Δm=1565 was constructed and tested. The major improvement in this new trap over that previously reported with m/Δm=324 [Rev. Sci. Instrum. 73, 2157 (2002)] was due to tighter machining tolerances of the hyperboloidal surfaces, with minor improvement due to better stability of the amplitude of the radio frequency trapping voltage. The present resolution is shown to be sufficient to separate clearly (to baseline) the following masses: 4He+ and D2+ (0.0256 u separation), 3He+ and H3+ (0.0074 u), 3He+ and HD+ (0.0059 u), and 4He2+ and H2+ (0.0143 u separation). Resolution of 4He+ and HT+ (0.0043 u separation) should also be possible, but was not carried out. Resolution of H3+ and HD+ (0.0015 u separation) is possible with peaks of comparable intensity, or with deconvolution.
Isothermal tuning of exchange bias using pulsed fields
Authors: Nogués J. , Sort J. , Suriñach S. , Muñoz J. S. , Baró M. D. , Bobo J. F. , Lüders U. , Haanappel E. , Fitzsimmons M. R. , Hoffmann A. , Cai J. W.
Published: May 2003

Exchange bias, HE, and coercivity, HC, of antiferromagnetic (AFM)/ferromagnetic bilayers can be adjusted, after deposition, at temperatures below the Néel temperature of the AFM by subjecting the samples to large pulsed fields (in excess of HPulse=550 kOe). The efficiency of the process depends on the AFM system and the direction of the applied field with respect of the unidirectional anisotropy direction. Textured (111) Fe19Ni81/Fe50Mn50 bilayers show an HE reduction and a HC increase when the pulse field is applied antiparallel to the unidirectional anisotropy, while they only exhibit a reduction in HC when the pulse is applied parallel to their unidirectional anisotropy. On the other hand, textured (111) NiO/Co bilayers exhibit a change of the angular dependence of HE when the pulse is applied away from the unidirectional anisotropy. The effects could be caused by field induced changes in the domain structure of the AFM or transitions in the AFM (spin–flop or AFM–paramagnetic).
Development of a coherent vacuum ultraviolet source at 104–108 nm generated by four-wave sum frequency mixing in Hg vapor
Authors: Kwon Chan Ho , Kim Hong Lae , Kim Myung Soo
Published: May 2003

A continuously tunable vacuum ultraviolet (VUV) light source in the 104–108 nm range has been developed by utilizing four-wave sum frequency mixing in Hg vapor. The windowless Hg cell designed uses a conelike glass capillary which transmits most of VUV generated while it restricts the flow of Hg and buffer gas. Usable power of about 109 photons/pulse (2 nJ/pulse) was obtained across the spectral region covered. The light source could be run for at least a month without maintenance and did not seem to contaminate the main apparatus.
A simple and efficient cryogenic loading technique for diamond anvil cells
Authors: Pravica Michael , Remmers Benjaman
Published: May 2003

We have developed a simple and time-efficient cryogenic loading technique for diamond anvil cells (DACs) using a glovebox. By using liquid nitrogen as a thermal reservoir to condense gaseous samples into the solid state, manually inserting the sample into an empty gasket, and then closing the DAC to seal a sample, we have easily loaded high-purity samples of carbon dioxide in less than 1 h. This technique has significant advantages over currently used methods to load cryogenic solids in both cost and time and can be used for a wide variety of solids with melting temperatures above 77 K.
Neutron sample cell suitable for the diffraction of aligned biomaterials and capable of exerting up to 370 MPa of hydrostatic pressure
Authors: Watson M. J. , Nieh M.-P. , Harroun T. A. , Katsaras J.
Published: May 2003

We describe a temperature controlled sample cell suitable for the study of biomimetic materials (e.g., lipid bilayers) using neutron diffraction, and capable of exerting hydrostatic pressures of up to 370 MPa. The advantage of this sample cell, compared to previous high-pressure cells of its type, is that it allows for the use of samples aligned on a solid support which, compared to “powder” or so-called liposomal preparations, requires only small amounts of sample and allows for the clear differentiation between in-plane and out-of-plane structure.
Combined Kerr microscope and magnetic force microscope for variable temperature ultrahigh vacuum investigations
Authors: Peterka D. , Enders A. , Haas G. , Kern K.
Published: May 2003

A new system combining a Kerr microscope and a magnetic force microscope for the study of magnetic domains in ultrathin films under ultrahigh vacuum conditions is presented. Due to the overlapping imaging range of both techniques magnetic domains can be investigated over a lateral range from millimeter down to fractions of a micrometer. Experiments can be done at variable temperatures, from 80 K to 600 K. First results are presented showing the same magnetic domain in a three monolayer Fe film on Cu (100) imaged with both techniques.
White light emission from radical carbonyl-terminations in Al2O3–SiO2 porous glasses with high luminescence quantum efficiencies
Authors: Hayakawa Tomokatsu , Hiramitsu Ai , Nogami Masayuki
Published: May 2003

Development of white phosphors with highly emissive, stable, and less toxic characteristics has been important for display and lighting technology. In this letter, it is shown that sol-gel-derived glasses of aluminosilicate composition, followed by a heat treatment in air at low temperatures around 500 °C, exhibit two intense, visible photoluminescence bands: One is due to point defects in these glasses and the other comes from radical carbonyl-terminations on the surface of pores. The photoluminescence provides a white light with high luminescence quantum efficiency (∼66.5%) under long-wavelength ultraviolet excitation.
Dielectric function of nanocrystalline silicon with few nanometers (<3 nm) grain size
Authors: Losurdo Maria , Giangregorio Maria Michela , Capezzuto Pio , Bruno Giovanni , Cerqueira M. F. , Alves E. , Stepikhova M.
Published: May 2003

The dielectric function of nanocrystalline silicon (nc-Si) with crystallite size in the range of 1 to 3 nm has been determined by spectroscopic ellipsometry in the range of 1.5 to 5.5 eV. A Tauc–Lorentz parameterization is used to model the nc-Si optical properties. The nc-Si dielectric function can be used to analyze nondestructively nc-Si thin films where nanocrystallites cannot be detected by x-ray diffraction and Raman spectroscopy.
A probe-positioning method with two-dimensional calibration pattern for micro-multi-point probes
Authors: Yashiro Wataru , Shiraki Ichiro , Miki Kazushi
Published: May 2003

A probe-positioning method for micro-multi-point probes that can be independently driven is proposed. By the electron-beam lithography technique, we fabricated a 0.5 mm×0.5 mm-sized probe-positioning pattern matrix consisting of 750 nm×750 nm-sized cells. Each cell has 150 nm×150 nm-sized pits that represent a bit array, which specifies its address. Reading the address information on the pattern with the microprobes allowed us not only to determine the probe positions, but also to calibrate the orientation and dimension of each scan.
Microspectroscopic two-dimensional Fermi surface mapping using a photoelectron emission microscope
Authors: Kotsugi M. , Kuch W. , Offi F. , Chelaru L. I. , Kirschner J.
Published: May 2003

We demonstrate the use of a photoelectron emission microscope in connection with a retarding field electron energy analyzer for the fast acquisition of two-dimensional momentum resolved photoelectron angular distribution patterns. This opens the possibility to combine spatial, momentum, and energy resolution of photoelectrons within the same instrument. We have applied this to observe the Cu(001) Fermi surface from a selected region of the sample. A well defined bulk Fermi surface is quickly mapped in this way.
First results of pinhole neutron imaging for inertial confinement fusion
Authors: Christensen C. R. , Barnes Cris W. , Morgan G. L. , Wilke M. , Wilson D. C.
Published: May 2003

Results are presented for the first implementation of pinhole imaging of inertial confinement fusion-produced neutrons. Raw images are shown, together with mathematical reconstructions of the source objects, for both spherical and asymmetric implosions. These reconstructions are considerably sharpened with respect to the raw images. They rely on the accurate calculation of the point-spread function, including neutron penetration into the material defining the pinhole. Proton recoil in the scintillator material and irregularity in scintillator fiber packing must be considered. The statistics of the system are inferred, which allows the use of simulations to demonstrate the robustness of the reconstructions to noise.
Techniques and mechanisms applied in electron cyclotron resonance sources for highly charged ions
Authors: Drentje A. G.
Published: May 2003

Electron cyclotron resonance ion sources are delivering beams of highly charged ions for a wide range of applications in many laboratories. For more than two decades, the development of these ion sources has been to a large extent an intuitive and experimental enterprise. Much effort has been spent in theoretical work, but a consistent description still is not available. From experimental activities, scaling rules have been formulated, which have successfully been used for the construction of more powerful devices. Special techniques like the coating of the plasma chamber walls, usage of secondary electron emission materials, installation of a biased probe or disk, and mixing the supply gas with other gas species, are generally being incorporated for improving the output of highly charged ions. Various ideas to understand these mechanisms have been brought up, again without consistent description. In experiments, the effect of the techniques with respect to physical parameters, i.e., reducing the plasma potential and/or lowering the ion temperature, has been demonstrated. In a recent study, the requirement of charge neutrality in the fluxes from the plasma to the walls of the plasma chamber has been evaluated; this shows that the occurrence of Simon currents in the conducting walls plays an important role in determining the value of the self-adjusting plasma potential. Most of the special techniques do affect the Simon currents, and therefore the plasma potential, thus the confinement. The effect of the gas mixing technique is mainly (but not exclusively) to decrease the ion temperature, and by that to increase the confinement. The present state of understanding the various techniques will be reviewed.
Very high long-term stability synchroscan streak camera
Authors: Uhring Wilfried , Zint Chantal Virginie , Summ Patrick , Cunin Bernard
Published: May 2003

In this article, we present the drifts phenomena that affect the temporal resolution of a standard synchroscan streak camera and some techniques to correct them in order to enhance the long-term resolution of these cameras. First, we give a comprehensive list of the components of the synchroscan streak camera which are sensitive to temporal and thermal drift: from the trigger circuit to the deflection plate of the tube. The way in which these components make the camera drift is explained and then quantified. A measure of drift realized on two streak cameras at the same time and in the same conditions (the same synchroscan signal) shows that each camera has its own intrinsic and stochastic drift. Second, two techniques to stabilize the camera are then described. The first method stabilizes the phase difference between the synchroscan signal and the deflection plate voltage. The second uses a laser reference trace on the phosphor screen and a digital data processing technique to reach the ultimate stability. The results show that a stabilized camera can be used immediately after it is turned on (due to suppression of the warm-up time) and still has very good temporal resolution even with a long-time exposure (2.4 ps full width at half maximum with a time exposure of 2 h has been achieved). This allows more exploration in the detection of very weak signals.
Development of a multiphoton fluorescence lifetime imaging microscopy system using a streak camera
Authors: Krishnan R. V. , Saitoh H. , Terada H. , Centonze V. E. , Herman B.
Published: May 2003

We report the development and detailed calibration of a multiphoton fluorescence lifetime imaging system (FLIM) using a streak camera. The present system is versatile with high spatial (∼0.2 μm) and temporal (∼50 ps) resolution and allows rapid data acquisition and reliable and reproducible lifetime determinations. The system was calibrated with standard fluorescent dyes and the lifetime values obtained were in very good agreement with values reported in the literature for these dyes. We also demonstrate the applicability of the system to FLIM studies in cellular specimens including stained pollen grains and fibroblast cells expressing green florescent protein. The lifetime values obtained matched well with those reported earlier by other groups for these same specimens. Potential applications of the present system include the measurement of intracellular physiology and fluorescence resonance energy transfer imaging, which are discussed in the context of live cell imaging.
Lasing characteristics and modal gain of a lateral-junction InGaAs/GaAs edge-emitting laser diode grown on a patterned GaAs (311) A-oriented substrate
Authors: Ocampo José M. Zanardi , Vaccaro Pablo O. , Saravanan Shanmugam , Kubota Kazuyoshi , Aida Tahito
Published: May 2003

Edge-emitting InGaAs/GaAs laser diodes were grown on patterned GaAs (311)A-oriented substrates. Due to the amphoteric properties of Si as a dopant in high-index GaAs, a device with a lateral p–n junction was obtained. CW lasing was observed up to 200 K. The dependence of the threshold current with temperature was measured. The characteristic temperatures were T0=180 and T0=57 K for experimental temperatures below and above 100 K, respectively, meaning that the carrier confinement structure must be improved. Quantitative results of the cavity gain were experimentally obtained.
Organic donor/acceptor photovoltaics: The role of C60/metal interfaces
Authors: Melzer Christian , Krasnikov Victor V. , Hadziioannou Georges
Published: May 2003

The photovoltaic properties of thin films based on donor/acceptor heterojunctions, prepared by means of either consecutive evaporation or co-evaporation, and sandwiched between asymmetric contacts are investigated. (E,E,E,E)-1,4-bis[(4-styryl)styryl]-2-methoxy-5-(2′-ethylhexoxy)benzene (MEH-OPV5) and Buckminster fullerene C60 are employed as donor and acceptor materials, respectively. Current-voltage measurements and impedance spectroscopy on the donor and the acceptor single-layer cells suggest the presence of a strong dipole layer at the C60/metal interfaces. The correlation between the photovoltaic performances and film morphologies is discussed.
Small-angle neutron scattering measurements of magnetic cluster sizes in magnetic recording disks
Authors: Toney Michael F. , Rubin Kurt A. , Choi Sung-Min , Glinka Charles J.
Published: May 2003

We describe small-angle neutron scattering measurements of the magnetic cluster size distributions for several longitudinal magnetic recording media. We find that the average magnetic cluster size is slightly larger than the average physical grain size, that there is a broad distribution of cluster sizes, and that the cluster size is inversely correlated to the media signal-to-noise ratio. These results show that intergranular magnetic coupling in these media is small and they provide empirical data for the cluster-size distribution that can be incorporated into models of magnetic recording.
Role of ultrathin Alq3 and LiF layers in conjugated polymer light-emitting diodes
Authors: Deng X. Y. , Tong S. W. , Hung L. S. , Mo Y. Q. , Cao Y.
Published: May 2003

We report that an ultrathin layer of tris-(8-hydroxyquinoline) aluminum (Alq3) interposed between a bilayer cathode of LiF/Al and an emissive layer can significantly improve electroluminescence efficiency in a polymer light-emitting device (PLED). At a current density of 35 mA/cm2, a poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenyl-enevinylene] (MEH-PPV)-based PLED with a cathode of Alq3/LiF/Al has a quantum efficiency of 2.5%, considerably higher than that of a MEH-PPV-based PLED with a bare Al or a LiF/Al cathode. Interfacial characteristics of MEH-PPV/LiF/Al and MEH-PPV/Alq3/LiF/Al were investigated by photoelectron spectroscopy, and the results were used to explain the difference in device performance.
Laser-diode-stimulated emission depletion microscopy
Authors: Westphal V. , Blanca C. M. , Dyba M. , Kastrup L. , Hell S. W.
Published: May 2003

We report subdiffraction resolution in far-field fluorescence microscopy through laser-diode-stimulated emission depletion of molecular markers. The diode-generated focal intensities lead to a resolution improvement by ∼45% in both lateral directions. Excitation and stimulated emission are performed with electronically synchronized diode pulses of 50–70 ps and 300–400 ps duration, respectively. The subdiffraction resolution is utilized to resolve neighboring individual molecules.
Tunable distributed feedback laser with photonic crystal mirrors
Authors: Mahnkopf S. , Kamp M. , Forchel A. , März R.
Published: May 2003

We report the development of a tunable laser diode based on InP using photonic crystal mirrors. The laser consists of two longitudinally coupled ridge waveguide segments that are coupled through a photonic crystal mirror segment. A laterally defined binary superimposed grating provides a distributed feedback in each of the cavities. Quasi-continuous tuning is achieved in a 24.5 nm window with 56 channels as typically required by wavelength division multiplexing applications.
Effect of low-temperature annealing on (Ga,Mn)As trilayer structures
Authors: Chiba D. , Takamura K. , Matsukura F. , Ohno H.
Published: May 2003

The effect of low-temperature annealing on (Ga,Mn)As/GaAs/(Ga,Mn)As trilayer structures is studied. Low-temperature annealing significantly increases the ferromagnetic transition temperature TC of top (Ga,Mn)As layers, reaching as high as 160 K, whereas no apparent effect is observed on bottom (Ga,Mn)As layers. The annealing effect on Be-doped trilayers is also presented.
4H–SiC photoconductive switching devices for use in high-power applications
Authors: Doǧan S. , Teke A. , Huang D. , Morkoç H. , Roberts C. B. , Parish J. , Ganguly B. , Smith M. , Myers R. E. , Saddow S. E.
Published: May 2003

Silicon carbide is a wide-band-gap semiconductor suitable for high-power high-voltage devices and it has excellent properties for use in photoconductive semiconductor switches (PCSSs). PCSS were fabricated as planar structures on high-resistivity 4H–SiC and tested at dc bias voltages up to 1000 V. The typical maximum photocurrent of the device at 1000 V was about 49.4 A. The average on-state resistance and the ratio of on-state to off-state currents were about 20 Ω and 3×1011, respectively. Photoconductivity pulse widths for all applied voltages were 8–10 ns. These excellent results are due in part to the removal of the surface damage by high-temperature H2 etching and surface preparation. Atomic force microscopy images revealed that very good surface morphology, atomic layer flatness, and large step width were achieved.
Electric-field-induced heating and energy relaxation in GaN
Authors: Eckhause T. A. , Süzer Ö. , Kurdak Ç. , Yun F. , Morkoç H.
Published: May 2003

Electric-field-induced heating is studied using noise measurements in n-type GaN grown on sapphire substrates. The measured electron temperature is found to be an order of magnitude higher than what is expected based on calculations of electron–phonon coupling via acoustic deformation potential scattering processes in GaN. The discrepancy may be explained by a large thermal boundary resistance between the GaN film and the sapphire substrate.
Influence of MgO substrate miscut on domain structure of pulsed laser deposited SrxBa1−xNb2O6 as characterized by x-ray diffraction and spectroscopic ellipsometry
Authors: Rouleau C. M. , Jellison G. E. , Beach D. B.
Published: May 2003

Pulsed laser deposition has been used to grow highly oriented SrxBa1−xNb2O6 (SBN:x) on (001)MgO and miscut MgO (2° off 001 toward 100) in the presence of a pulsed O2 jet. The target stoichiometry was SBN:52±1.5%, but films grown at 700 °C were cation deficient and had a final composition of SBN:61±1.5%. Visually, the films were specular, but spectroscopic ellipsometry measurements showed they were highly absorbing, requiring a short anneal in O2 at 700 °C to make them fully transparent. Pole figure analysis indicated that a thick 626±1 nm film consisted of the characteristic antiphase domain structure of SBN, but four antiphase domains were found in a thin 185±1 nm film. However, the formation of these additional domains was suppressed in a 165±1 nm film grown on miscut MgO. Spectroscopic ellipsometry measurements have been made to measure surface and interface roughness, film thickness, as well as the spectroscopic refractive index and extinction coefficient of the films.
Very efficient light emission from bulk crystalline silicon
Authors: Trupke Thorsten , Zhao Jianhua , Wang Aihua , Corkish Richard , Green Martin A.
Published: May 2003

Due to its indirect bandstructure, bulk crystalline silicon is generally regarded as a poor light emitter. In contrast to this common perception, we report here on surprisingly large external photoluminescence quantum efficiencies of textured bulk crystalline silicon wafers of up to 10.2% at T=130 K and of 6.1% at room temperature. Using a theoretical model to calculate the escape probability for internally generated photons, we can conclude from these experimental figures that the radiative recombination probability or internal luminescence quantum efficiency exceeds 20% at room temperature.