bluuebunny/crossref_metadata_2025 huggingface dataset:
Enteric Bacterial Catalysts for Fuel Ethanol Production
Authors: Ingram L. O. , Aldrich H. C. , Borges A. C. C. , Causey T. B. , Martinez Alfredo , Morales Fernando , Saleh Alif , Underwood S. A. , Yomano L. P. , York S. W. , Zaldivar Jesus , Zhou Shengde
Published: July 2002

The technology is available to produce fuel ethanol from renewable lignocellulosic biomass. The current challenge is to assemble the various process options into a commercial venture and begin the task of incremental improvement. Current process designs for lignocellulose are far more complex than grain to ethanol processes. This complexity results in part from the complexity of the substrate and the biological limitations of the catalyst. Our work at the University of Florida has focused primarily on the genetic engineering of Enteric bacteria using genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase. These two genes have been assembled into a portable ethanol production cassette, the PET operon, and integrated into the chromosome of Escherichia coli B for use with hemicellulose‐derived syrups. The resulting strain, KO11, produces ethanol efficiently from all hexose and pentose sugars present in the polymers of hemicellulose. By using the same approach, we integrated the PET operon into the chromosome of Klebsiella oxytoca to produce strain P2 for use in the simultaneous saccharification and fermentation (SSF) process for cellulose. Strain P2 has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cellulase enzymes. Recently, the ability to produce and secrete high levels of endoglucanase has also been added to strain P2, further reducing the requirement for fungal cellulase. The general approach for the genetic engineering of new biocatalysts using the PET operon has been most successful with Enteric bacteria but was also extended to Gram positive bacteria, which have other useful traits for lignocellulose conversion. Many opportunities remain for further improvements in these biocatalysts as we proceed toward the development of single organisms that can be used for the efficient fermentation of both hemicellulosic and cellulosic substrates.
Stabilization of a tyrosine O‐sulfate residue by a cationic functional group: formation of a conjugate acid–base pair
Authors: Yagami T. , Kitagawa K. , Aida C. , Fujiwara H. , Futaki S.
Published: July 2002

Abstract: Sulfated tyrosine [Tyr(SO3H)]‐containing peptides showed characteristic peak patterns in their liquid secondary‐ion mass spectrometry (LSIMS) spectra. Protonated molecules were desulfated more easily than their deprotonated counterparts. Therefore, the stabilities of the Tyr(SO3H) residues were well‐reflected by peak patterns in their positive‐ion spectra. These intrinsic peak patterns were investigated by comparing the behavior of each Tyr(SO3H) residue in acidic solution. As the peptide chain was lengthened and the number of cationic functional groups increased, the peak representing the [MH]+ of a Tyr(SO3H)‐containing peptide became more prominent than that representing the desulfated [MH–SO3]+. These alterations in peptide structure also increased the stability of the Tyr(SO3H) residue in acidic solution. Based on the desulfation mechanism of an aryl monosulfate, we predicted that intramolecular cationic functional groups would stabilize Tyr(SO3H) residues by forming conjugate acid–base pairs (or salt bridges) both in the gaseous phase and in acidic solution. In accordance with this theory, Arg residues would take primary responsibility for this self‐stabilization within Tyr(SO3H)‐containing peptides. Moreover, a long peptide backbone was expected to have a weak protective effect against desulfation of the [MH]+ in the gaseous phase. Tyr(SO3H) residues were also stabilized by adding an external basic peptide containing multiple Arg residues. Formation of such intermolecular acid–base pairs was demonstrated by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) which detected conjugated peptide ions. The energetically favorable formation of conjugate acid–base pairs prompted by Tyr(SO3H) residues might be a driving force for protein folding and protein–protein interaction.
Phosphorylation and activation of mitogen- and stress-activated protein kinase-1 in adult rat cardiac myocytes by G-protein-coupled receptor agonists requires both extracellular-signal-regulated kinase and p38 mitogen-activated protein kinase
Authors: MARKOU Thomais , LAZOU Antigone
Published: July 2002

G-protein-coupled receptor agonists are powerful stimulators of mitogen-activated protein kinase (MAPK) cascades in cardiac myocytes. However, little is known regarding the physiological activation of enzymes downstream of MAPKs. We examined the activation of mitogen- and stress-activated protein kinase-1 (MSK1), a downstream target of MAPKs, in adult rat cardiac myocytes by phenylephrine and endothelin-1. Both agonists induced the phosphorylation of MSK1 at Thr-581 and Ser-376 but not at Ser-360. Maximal phosphorylation was observed at 10–15min after stimulation and it correlated with increased activity. Maximal activation of MSK1 in adult cardiomyocytes temporally coincided with maximal p38 MAPK activation while activation of the extracellular-signal-regulated kinase (ERK) cascade was more rapid. Phosphorylation and activation of MSK1 was completely inhibited by either PD98059 (ERK1/2 pathway inhibitor) or SB203580 (p38 MAPK inhibitor) alone. These data demonstrate that MSK1 activation in adult rat cardiac myocytes by G-protein-coupled receptor agonists requires the simultaneous activation of both the ERK and p38 MAPK pathways. However, the lack of phosphorylation at Ser-360, an identified phosphorylation site targeted by MAPKs, may indicate that MSK1 is not a direct substrate of ERK1/2 and p38 MAPK in adult rat cardiomyocytes.
Mutational analysis of the C‐domain in nonribosomal peptide synthesis
Authors: Bergendahl Veit , Linne Uwe , Marahiel Mohamed A.
Published: July 2002

The initial condensation event in the nonribosomal biosynthesis of the peptide antibiotics gramicidin S and tyrocidine␣A takes place between a phenylalanine activating racemase GrsA/TycA and the first proline‐activating module of GrsB/TycB. Recently we established a minimal in vitro model system for NRPS with recombinant His6‐tagged GrsA (GrsAPhe‐ATE; 127 kDa) and TycB1 (TycB1Pro‐CAT; 120 kDa) and demonstrated the catalytic function of the C‐domain in TycB1Pro‐CAT to form a peptide bond between phenylalanine and proline during diketopiperazine formation (DKP). In this work we took advantage of this system to identify catalytically important residues in the C‐domain of TycB1Pro‐CAT using site‐directed mutagenesis and peptide mapping. Mutations in TycB1Pro‐CAT of 10 strictly conserved residues among 80 other C‐domains with potential catalytic function, revealed that only R62A, H147R and D151N are impaired in peptide‐bond formation. All other mutations led to either unaffected (Q19A, C154A/S, Y166F/W and R284A) or insoluble proteins (H146A, R67A and W202L). Although 100 nm of the serine protease inhibitors N‐α‐tosyl‐l‐phenylalanylchloromethane or phenylmethanesulfonyl fluoride completely abolished DKP synthesis, no covalently bound inhibitor derivatives in the C‐domain could be identified by peptide mapping using HPLC‐MS. Though the results do not reveal a particular mechanism for the C‐domain, they exhibit a possible way of catalysis analogous to the functionally related enzymes chloramphenicol acetyltransferase and dihydrolipoyl transacetylase. Based on this, we propose a mechanism in which one catalytic residue (H147) and two other structural residues (R62 and D151) are involved in amino‐acid condensation.
Aggression and competition for shelter between a native and an introduced crayfish in Europe
Authors: Vorburger Christoph , Ribi Georg
Published: July 2002

1. The introduced North American crayfish, Pacifastacus leniusculus Dana, is expanding its range in Europe and locally often replaces two native crayfish species, Astacus astacus L. and Austropotamobius pallipes Lereboullet. Pacifastacus leniusculus is also expected to invade the habitat of a third native crayfish, the endangered Austropotamobius torrentium Schrank. Interspecific aggressive interactions and competition for shelter were experimentally studied in the laboratory to assess the potential impact of P. leniusculus on A. torrentium.

2. Neither species was inherently dominant in aggressive interactions, but dominance was strongly size‐dependent, favouring the larger and faster growing species, P. leniusculus.

3. Access to limited shelter was generally determined by aggressive dominance, although species‐specific preference also influenced the outcome of competition for shelter. Austropotamobius torrentium had a higher preference for experimental shelters and often defended these even against larger P. leniusculus.

4. In accordance with theoretical models of animal conflicts, agonistic interactions between equally sized contestants were more severe than between animals of different size.

5. The P. leniusculus used in the present experiment were infected with the crayfish plague, Aphanomyces astaci, to which the animals are resistant. The crayfish transmitted the disease to non‐resistant A. torrentium which died ≈ 2 weeks after contact with P. leniusculus.
Differential mRNA Expression of the Two Mineralocorticoid Receptor Splice Variants Within the Human Brain: Structure Analysis of their Different DNA Binding Domains
Authors: Wickert L. , Selbig J. , Watzka M. , Stoffel‐Wagner B. , Schramm J. , Bidlingmeier F. , Ludwig M.
Published: July 2002

In human brain tissue, cortisol action, at basal concentrations, is mediated by the mineralocorticoid receptor (MR). An in‐frame insertion of 12 bp in the MR‐DNA‐binding domain due to alternative splice site usage between exons 3 and 4 results in an MR mRNA splice variant (MR+4) encoding a receptor protein with four additional amino acids compared to the wild‐type MR protein. To elucidate the questions of sex, age, and/or tissue dependent differences of the relative amount of the two mRNA subtypes, we examined 131 fresh human brain tissue samples from temporal and frontal lobe or hippocampus. One hundred and twenty samples were obtained from patients with epilepsy and 11 samples from patients with brain tumours. A small but signi®cant difference of the MR+4 mRNA splice variant proportions in cortex (9.5t0.8%) and subcortical white matter (6.6t0.7%) of the temporal lobe could be detected, indicating differential MR splice variant expression within these brain areas. Moreover, the splice variant ratios in samples of the temporal lobe cortex collected from patients with epilepsy differed from samples of patients with brain tumours. These data point to an altered expression of the MR splice variants in epilepsy, and strengthen the supposition of a tissue speci®c alternative splicing of the MR mRNA. The frequent occurence of the MR+4 transcript raises the question of its functional signi®cance. For this reason, an MR+4 DNA‐binding‐domain structure model was generated by computer‐based homology modelling based on the known glucocorticoid receptor structure. The data obtained revealed no distorting effect of the inserted four amino acids on the adjacent secondary structures, thereby suggesting that both zinc ®ngers retain their function. The resulting structure of the MR+4 model leads to the supposition that the receptor retains its function. Moreover, databank analysis with respect to this kind of steroid receptor variation and our own sequence data of the closely related progesterone receptor sustained the hypothesis that only corticosteroid receptors were affected by this alternative splicing event.
Fulminant hepatitis and the new G/GBV‐C flavivirus
Authors: Hadziyannis S. J.
Published: July 2002

A new virus within the family Flaviviridae, ‘hepatitis’ G/GBV‐C, has been incriminated by several authors as a causative factor of idiopathic or cryptogenic fulminant hepatitis, a syndrome of presumed viral aetiology. Review of worldwide data from 22 studies on 364 cases indicates that G/GBV‐C infection is present in approximately 20% of idiopathic cases but a similar or even higher prevalence is detected in fulminant hepatitis of viral B, D or C aetiology, reflecting a high rate of parenteral viral exposure rather than a specific aetiology of fulminant hepatic failure. An aetiopathogenic role of G/GBV‐C in fulminant hepatitis seems to be further refuted by the analysis of other data in the literature. The presence of G/GBV‐C infection in fulminant hepatic failure is largely a result of secondary infection or coinfection. The aetiopathogenetic mystery of cryptogenic or idiopathic fulminant hepatitis remains unsolved.
Phosphoinositide‐dependent activation of Rho A involves partial opening of the RhoA/Rho‐GDI complex
Authors: Fauré Julien , Vignais Pierre V. , Dagher Marie‐Claire
Published: July 2002

Rho GTPases have two interconvertible forms and two cellular localizations. In their GTP‐bound conformation, they bind to the cell membrane and are activated. In the inactive GDP‐bound conformation, they associate with a cytosolic protein called GDP dissociation inhibitor (GDI). We previously reported that the RhoA component of the RhoA/Rho‐GDI complex was not accessible to the Clostridium botulinum C3 ADP‐ribosyl transferase, unless the complex had been incubated with phosphoinositides. We show here that PtdIns, PtdIns4P, PtdIns3,4P2, PtdIns4,5P2 and PtdInsP3 enhance not only the C3‐dependent ADP‐ribosylation, but also the GDP/GTP exchange in the RhoA component of the prenylated RhoA/Rho‐GDI complex. In contrast, in the nonprenylated RhoA/Rho‐GDI complex, the levels of ADP‐ribosylation and GDP/GTP exchange are of the same order as those measured on free RhoA and are not modified by phosphoinositides. In both cases, phosphoinositides partially opened, but did not fully dissociate the complex. Upon treatment of the prenylated RhoA/Rho‐GDI complex with phosphoinositides, a GTP‐dependent transfer to neutrophil membranes was evidenced. Using an overlay assay with the prenylated RhoA/Rho‐GDI complex pretreated with PtdIns4P and labeled with [α32P]GTP, three membrane proteins with molecular masses between 26 and 32 kDa were radiolabeled. We conclude that in the presence of phosphoinositides, the prenylated RhoA/Rho‐GDI complex partially opens, which allows RhoA to exchange GDP for GTP. The opened GTP‐RhoA/Rho‐GDI complex acquires the capacity to target specific membrane proteins.
Endoscopic treatment for urinary incontinence in children with a congenital neuropathic bladder
Authors: Silveri  , Capitanucci  , Mosiello  , Broggi  , DE Gennaro
Published: July 2002

Objective

 To verify, in a retrospective analysis, the effectiveness of endoscopic treatment (collagen injection) in children with neurogenic bladder and neurogenic urinary incontinence.

Patients and methods

 From January 1992 to March 1997, 36 endoscopic collagen injections were performed to treat neurogenic urinary incontinence in 23 patients (mean age 10.9 years, range 6–17 at the time of the first procedure) selected on the basis of clinical status and the patient’s motivation. Nineteen patients were affected by myelomeningocele and four had an occult spinal dysraphism. All patients underwent a preoperative cystometric urodynamic evaluation (without urethral pressure measurement) which showed detrusor areflexia in 12, normal reflexia in one and hyper‐reflexia in 10 patients. Bladder compliance was considered good (≥20 cmH2O) in 13 patients and low (10–20 cmH2O) in 10, four of whom had detrusor areflexia. Twenty‐one children emptied their bladder by intermittent clean catheterization. The mean (range) follow‐up was 19.2 (6–54) months. Twenty (group A) and 16 (group B) procedures, performed early and late in the series, were analysed separately to determine any increase in effectiveness with surgical experience. The evaluation criteria were; the increase in the ‘dry’ interval (between catheterizations) before and after treatment/s (Δdry); the patient’s and parent’s satisfaction; the number of endoscopic procedures and quantity of injected materials.

Results

 There was an improvement (dryness of at least 2 h; Δdry of 1 h) in 13 of 23 patients after 1–3 (mean 1.5) procedures; 10 patients had a 0.2 h increase in Δdry after 1–3 injections and none was satisfied. There was no difference in the Δdry (0.9 vs. 0.7 h) between groups A and B, and/or the patient’s/parent’s satisfaction. Success rates differed with urodynamic patterns; seven of 10 patients showing no improvement had hyper‐reflexia and three of the remaining 12 with areflexia had hypocompliant bladders, while nine of the 13 showing improvement had an areflexic detrusor and low‐pressure bladders.

Conclusion

 The efficacy of the treatment depends largely on the urodynamic selection of patients (mainly those with detrusor areflexia and good compliance). The outcome may be improved further by increasing the quantity of injected material and with a longer follow‐up, performing the procedure again if advisable. A close postoperative clinical (pad test) and personal observation is necessary to evaluate the outcome and thus optimize the strategy of treatment.
The histology and immunohistochemistry of free buccal mucosa and full‐skin grafts after exposure to urine
Authors: Filipas D. , Fisch M. , Fichtner J. , Fitzpatrick J. , Berg K. , Störkel S. , Hohenfellner R. , Thüroff J. W.
Published: July 2002

Objective

To investigate the histological and immunohistochemical behaviour of free buccal mucosa and fullskin grafts after exposure to urine.

Materials and methods

A buccal mucosal graft and a full‐skin graft were freely transferred into the bladder of 12 minipigs, after stripping the bladder mucosa. Endoscopic investigations were carried out 2 and 5 months after surgery, and the grafts examined after death at 7 months, both histologically and immunohi‐stochemically.

Results Shrinkage

Shrinkage of the full‐skin graft was apparent endoscopically in five cases. Of the nine full‐skin grafts, four showed severe inflammatory reactions, two necrosis and two ulcerations. Conversely, the 10 buccal mucosal grafts had fewer pathological findings (three minimal inflammation and three with scars) and a pronounced similarity on immunofullhistochemistry.

Conclusions

The buccal mucosal graft showed significantly fewer adverse histopathological findings after long‐term exposure to urine than the full‐skin graft and is therefore a preferable material for urethral reconstruction.
Increased aortic stiffness in women with Type 1 diabetes mellitus is associated with diabetes duration and autonomic nerve function
Authors: Ahlgren Å. Rydén , Sundkvist G. , Wollmer P. , Sonesson B. , Lärme T.
Published: July 2002

Aims

The increase in risk for cardiovascular complications in diabetic women is even greater than that in diabetic men. We found arterial stiffness to be increased in women, but not in men, with Type 1 diabetes mellitus (DM). The aims of the present study were to evaluate whether the changes in arterial distensibility are influenced by diabetes duration and to evaluate any association between autonomic neuropathy and decreased arterial distensibility.

Methods

Stiffness of the abdominal aorta was measured noninvasively using echo‐tracking sonography and parasympathetic function by heart rate variation during deep breathing (E/I ratio) in 40 women (mean age 33 years, range 20‐61) and 38 men (mean age 36 years, range 22‐56) with Type 1 DM.

Results

There was a significant correlation between aortic stiffness and duration of diabetes in women (r = 0.41, P = 0.008), but not in men (r = 0.15, P = 0.35). There was also a significant correlation between aortic stiffness and the E/I ratio in women (r = ‐0.49, P = 0.002), but not in men (r = ‐0.14, P = 0.41). When adjusted for diabetes duration, the significant association between the E/I ratio and aortic stiffness remained in diabetic women (r = ‐0.44, P = 0.008) and was stronger than the association between diabetes duration and aortic stiffness. There were no significant correlations between aortic stiffness and triglycerides or total cholesterol, respectively.

Conclusions

Increased aortic wall stiffness found in women with Type 1 DM is related to diabetes duration. Further, in women with Type 1 DM there is a correlation between increased aortic stiffness and parasympathetic dysfunction. This may be of importance for the increased susceptibility to cardiovascular complications in diabetic women.
Care of Patients Nearing Death: Another View
Authors: Finucane Thomas E.
Published: July 2002

A person with an advanced, progressive, ultimately fatal illness faces multifaceted suffering. It is difficult to be sick. Uncontrollable deterioration of one's body can be horrible. Many people detest seeking help from others, yet nearly all want companionship in the face of death. The choice is hard, between certain death, even if it is promised to be comfortable and dignified, and hope, even if it is a burdensome treatment that offers small chance of limited benefit. Dying patients are often expected to make such painful choices. Perhaps what is most painful is to be dying. A person whose near future necessarily contains all this will often need a trusted, unhurried companion, acting with gentle advocacy and humility. This paper offers perspective and suggestions to such companions/advocates.
Lumbar catheterization of the subarachnoid space with a 32‐gauge polyurethane catheter in the rat
Authors: Pogatzki Esther M. , Zahn Peter K. , Brennan Timothy J.
Published: July 2002

Chronic catheterization of the subarachnoid space of rats is an important tool for intrathecal drug delivery in pharmacologic investigations of pain. We describe a technique using direct lumbar insertion of a small 32‐gauge polyurethane (PU) catheter without extensive surgery. Location of the catheter was confirmed with 2% lidocaine injection 1 day later, and methylene blue injection after 7–14 days. This method improved recovery of the rat after catheter implantation and reduced neurologic complications. Copyright 2000 European Federation of Chapters of the International Association for the Study of Pain
Gender differences in regional brain response to visceral pressure in IBS patients
Authors: Berman Steven , Munakata Julie , Naliboff Bruce D. , Chang Lin , Mandelkern Mark , Silverman Dan , Kovalik Edward , Mayer Emeran A.
Published: July 2002

In two experiments including a total of 30 irritable bowel syndrome patients, symptom‐mimicking rectal pressure stimuli elicited changes in regional neural activation as measured by positron electron tomography (PET) cerebral blood flow images. Although most stimuli were not rated as painful, rectal pressure increased regional cerebral blood flow (rCBF) in areas commonly associated with somatic pain, including the anterior cingulate, insula, prefrontal cortex, thalamus, and cerebellum. Despite similar stimulus ratings in male and female patients, regional activations were much stronger for males. In both experiments, rectal pressure activated the insula bilaterally in males but not in females. Insula activation was associated most strongly with objective visceral pressure, whereas anterior cingulate activation was associated more with correlated ratings of subjective discomfort. The insula is discussed as a visceral sensory cortex. Several possible reasons for the insula gender effect are proposed.
Low-temperature processing of titanium nitride films by laser physical vapor deposition
Authors: Biunno N. , Narayan J. , Hofmeister S. K. , Srivatsa A. R. , Singh R. K.
Published: July 2002

We have investigated the formation of polycrystalline TiN films on (100) Si substrates using a low-temperature laser processing method. The films were deposited by laser ablation of a TiN hot-pressed pellet in the presence of neutral or ionized nitrogen using a XeCl excimer laser (wavelength 308 nm, pulse duration 45×10−9 s, and energy density of 4–5 J cm−2). The substrate temperature ranged from 25 to 550 °C. Plan-view and cross-section transmission electron microscopy studies show that the films are polycrystalline (average grain size ∼100 Å) with face-centered-cubic structure and lattice constant of 4.25 Å. It is interesting to note that the average grain size remained approximately constant with substrate temperature up to 550 °C. Chemical composition was analyzed by Rutherford backscattering and Auger electron spectroscopy as a function of film depth. The results show that the films reproduced closely the chemical composition of the TiN target which contained some oxygen, and that the oxygen content decreased with increased substrate temperature. Four-point probe measurements and I-V characteristics show that the films are metallic with a typical resistivity of ∼150 μΩ cm. The microhardness values of these films were found to be as high as 17 GPa.
Fast bolometric response by high Tc detectors measured with subnanosecond synchrotron radiation
Authors: Carr G. L. , Quijada M. , Tanner D. B. , Hirschmugl C. J. , Williams G. P. , Etemad S. , Dutta B. , DeRosa F. , Inam A. , Venkatesan T. , Xi X.
Published: July 2002

We have measured a fast response by thin-film YBa2Cu3O7−δ detectors to pulsed, broadband, infrared radiation. Synchrotron light from an electron storage ring was used as the infrared source, providing subnanosecond pulses from far infrared through visible. Pulse responsivities as high as 106 V/J and as fast as 4 ns have been observed. For film thicknesses in the range 400–3200 Å, the detector response follows the film absorptivity while the speed varies inversely with thickness, suggesting a bolometric mechanism. Calculations based on such a model are in accord with the data. We find no evidence for any nonbolometric components in the response.
High critical currents in strained epitaxial YBa2Cu3O7−δ on Si
Authors: Fork D. K. , Fenner D. B. , Barton R. W. , Phillips Julia M. , Connell G. A. N. , Boyce J. B. , Geballe T. H.
Published: July 2002

Epitaxial YBa2Cu3O7−δ (YBCO) films were grown on Si (100) using an intermediate buffer layer of yttria-stabilized zirconia. Both layers are grown via an entirely in situ process by pulsed laser deposition. All films consist of c-axis oriented grains as measured by x-ray diffraction. Strain results from the large difference in thermal expansion coefficients between Si and YBCO. Thin (<500 Å) YBCO films are unrelaxed and under tensile strain with a distorted unit cell. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield for Ba as low as 12%. The normal-state resistivity is 280 μΩ cm at 300 K; the critical temperature Tc (R=0) is 86–88 K with a transition width (ΔTc) of 1 K. Critical current densities of 2×107 A/cm2 at 4.2 K and 2.2×106 A/cm2 at 77 K have been achieved.
Delay-time measurements in narrowed waveguides as a test of tunneling
Authors: Ranfagni A. , Mugnai D. , Fabeni P. , Pazzi G. P.
Published: July 2002

Delay-time measurements with a microwave setup, where a step narrowing in the waveguide simulates a quantum mechanical potential barrier, have been performed even beyond the cutoff. This allows experimental measurements in a very accessible temporal range of the order of nanoseconds. The results, interpreted as tunneling times, are compared with the existing quantum mechanical models, translated into the electromagnetic framework.
Silicon Mach–Zehnder waveguide interferometers based on the plasma dispersion effect
Authors: Treyz G. V. , May P. G. , Halbout Jean-Marc
Published: July 2002

Silicon Mach–Zehnder waveguide modulators have been fabricated and operation characterized at the wavelength of 1.3 μm. Device operation is based on the free-carrier-induced change in the refractive index of silicon. Modulation depths of −4.9 dB and response times τresponse<50 ns have been achieved at λ=1.3 μm for an injected carrier density of 6.5×1017 cm−3.
Polymer films formed with monolayer growth steps by molecular layer deposition
Authors: Yoshimura Tetsuzo , Tatsuura Satoshi , Sotoyama Wataru
Published: July 2002

Molecular layer deposition is the process in which molecules are stacked on substrates one by one in order of preference in a vacuum. We studied the possibility using two kinds of molecules: pyromellitic dianhydride (A) and 2,4-diaminonitrobenzene or 4,4′-diaminodiphenyl ether (B). After forming a layer consisting of A (or B), we supplied molecule B (or A). The film rapidly thickened and became saturated in 10–60 s. The change in thickness induced in this step was about 5 Å, close to the size of the molecules involved. This indicates that a monomolecular layer of B (or A) grew on layer A (or B) and film growth self-terminated automatically. 15 steps of alternately supplying A and B produced a polymer film 100 Å thick.
Externally pumped high repetition rate femtosecond infrared optical parametric oscillator
Authors: Mak Gary , Fu Qiang , van Driel Henry M.
Published: July 2002

The first externally pumped high repetition rate optical parametric oscillator (OPO) which produces tunable femtosecond pulses in the near-infrared is demonstrated. The singly resonant oscillator with a KTiOPO4 (KTP) nonlinear crystal is synchronously pumped by 150-fs pulses at 645 nm from a mode-locked dye laser. With a pump power of 280 mW, stable 220-fs pulses at a 76-MHz repetition rate, tunable from 1.20 to 1.34 μm with a single set of mirrors, are achieved. The internal power conversion efficiency is 13% and the average infrared power is as large as 30 mW, for the signal beam only. Femtosecond pulses tunable over the wavelength range from 0.9–4.5 μm (with KTP) using multiple mirror sets should be possible. This range includes the technologically important regime from 1.0–1.6 μm.
Terahertz optical rectification from a nonlinear organic crystal
Authors: Zhang X.-C. , Ma X. F. , Jin Y. , Lu T.-M. , Boden E. P. , Phelps P. D. , Stewart K. R. , Yakymyshyn C. P.
Published: July 2002

We report optical rectification and subsequent generation of subpicosecond submillimeter-wave radiation from a nonlinear organic crystalline salt. With optical excitation at a wavelength of 820 nm and a 150 fs pulse duration, the magnitude of the rectified field from the organic salt dimethyl amino 4-N-methylstilbazolium tosylate is one and two orders of magnitude larger than that from GaAs and LiTaO3 crystals, respectively. This organic crystal presently provides the most intense terahertz radiated field among all of the natural nonexternally biased materials we know.
Giant magnetoresistance in melt spun Cu-Co alloys
Authors: Wecker J. , von Helmolt R. , Schultz L. , Samwer K.
Published: July 2002

Cu1−xCox alloys with x=0.1 and x=0.2 have been prepared by conventional melt spinning. The rapid solidification process results in an extended solubility of Co in Cu although some Co precipitates already during quenching. In the as-quenched ribbons, the magnetoresistance (MR) is only of the order of 1.5%. It increases dramatically with the controlled nucleation and growth of Co precipitates from the supersaturated Cu matrix. The highest MR of 11% at 300 K occurs for Cu90Co10 after an aging at about 440 °C when the Co clusters are superparamagnetic. Saturation is possible only after a higher annealing or at lower measuring temperatures. For the optimally annealed samples the MR increases to 36% at 30 K.
Noncontact determination of transverse isotropic elastic moduli in polyimide thin films using a laser based ultrasonic method
Authors: Rogers John A. , Dhar Lisa , Nelson Keith A.
Published: July 2002

A transient grating laser ultrasonic method known as real-time impulsive stimulated thermal scattering is used to excite and monitor Lamb acoustic waveguide modes in free-standing thin polyimide films which are known to have transverse isotropic symmetry. The dispersion of these Lamb modes is used to accurately evaluate both the in and out-of-plane elastic moduli.
Growth and properties of La2−xSrxCuO4 films
Authors: Trofimov I. E. , Johnson L. A. , Ramanujachary K. V. , Guha S. , Harrison M. G. , Greenblatt M. , Cieplak M. Z. , Lindenfeld P.
Published: July 2002

Single-crystalline films of La2−xSrxCuO4 have been grown epitaxially on SrTiO3, NdGaO3, and LaSrAlO4 substrates by laser ablation. We show that record values of the superconducting transition temperature may be achieved by high-pressure annealing in oxygen. The films exhibit values of Tco above 38 K, as well as a linear variation of the resistivity with T and excellent crystal quality.
In situ thin film thickness measurement with acoustic Lamb waves
Authors: Pei Jun , Degertekin F. Levent , Khuri-Yakub Butrus T. , Saraswat Krishna C.
Published: July 2002

In situ thin film thickness measurement is an important problem in semiconductor processing, which is currently limited by the lack of adequate sensors. Most of today’s available techniques are restricted to certain type of films and many have difficulties in performing the measurement in situ. The fact that the velocity of an ultrasonic Lamb wave traveling in a silicon wafer is changed by the thin film coating on the wafer surface can be used as a monitoring method for basically any type of film—opaque, transparent, metal, or insulator. The acoustic sensors are easily implemented into plasma or CVD environments. We have demonstrated the technique in an aluminum sputtering system in which we measure Al film thickness with a resolution of ±100 Å. Even better resolution can be achieved for SiO2, copper, and tungsten films. This system has a variety of potential applications, not only in film thickness measurement, but also in characterization of film properties and multilayer deposition process control.
Reactivity at the Al/Si3N4 interfaces
Authors: Avila J. , Sacedón J. L.
Published: July 2002

The reactivity of the Al/Si3N4/Si(100) system has been studied using x-ray photoelectron spectroscopy (XPS). The Si3N4 overlayer was prepared on Si(100) by N ion implantation and subsequent annealing. The deposition at 673 K of Al on a 18 Å Si3N4 overlayer leads to the total reduction of the Si3N4 overlayer and the aluminum nitridation. The reaction also takes place at room temperature (RT) but to a lesser degree. The stability of a RT formed Al/Si3N4/Si structure was examined by increasing the sample temperature up to 673 K. In this way, the near complete reduction of a 24 Å Si3N4 overlayer was obtained. These results show the instability of the Al/Si3N4 interface at moderate annealing temperatures.
Double crystal monochromator for synchrotron radiation with decreased radiation power density
Authors: Hrdý Jaromir
Published: July 2002

It is suggested to use the double crystal monochromator (spectrometer) having finite angle between diffracting planes and the surface of the crystals to increase the irradiated area on the first crystal. In both crystals the plane determined by the impinging beam and the normal to the diffracting planes is perpendicular to the plane determined by the normals to the diffracting planes and to the surface of the crystal, so that the diffraction remains symmetrical. The advantage of this system is that the range of Bragg angles is limited only by the dimensions of the crystals.
New technique of measuring dendrite growth velocities in undercooled metallic melts
Authors: Eckler K. , Kratz M. , Egry I.
Published: July 2002

A new technique is developed and described which allows the measurement of dendrite growth velocities in undercooled melts in an electromagnetic levitation facility. The triggering of nucleation at the bottom of the liquid drop (=beginning of growth at t=t*) and the end of recalescence (=end of growth at t=t++) are detected by a capacitance proximity sensor and a photodiode, respectively. Dendrite growth velocities are determined as the ratio 2R0/(t++−t*), where 2R0 denotes the vertical diameter of the drop. First results on pure Ni demonstrate the capability of the method to produce less scattered data than other techniques.
Three-wire thermocouple: Frequency response in constant flow
Authors: Forney L. J. , Fralick G. C.
Published: July 2002

Theory and experimental measurements are compared with a novel three-wire thermocouple. Signals from three wires of unequal diameters are recorded from the thermocouple suspended in constant flow with a periodic temperature fluctuation. It is demonstrated that the reconstructed signal from the three-wire thermocouple requires no compensation for ω≤5ω1, where ω1 is the natural frequency of the smaller wire. The latter result represents a significant improvement compared to previous work with two-wire thermocouples. A correction factor has also been derived to account for wires of arbitrary diameter.
Polarization-modulated Raman scattering measurements of nematic liquid crystal orientation
Authors: Huang Kelly , Archer Lynden A. , Fuller Gerald G.
Published: July 2002

This article presents a new, automated Raman scattering experiment to measure the orientation in nematic liquid crystals. The automated experiment utilizes phase modulation to alter the polarization state of light unlike conventional, polarized Raman experiments which require the manual manipulation of polarizers and multiple measurements. Polarization modulation imparts the ability to quantify the second and fourth moments of the orientation distribution function with a single measurement. The feasibility of the new experiment is demonstrated through orientation measure- ments of a well characterized nematic liquid crystal, 4-pentyl-(4-cyanophenyl)-cyclohexane. Additionally, since the results of the polarization-modulated technique are in excellent agreement with conventional Raman measurements, this study supports the validity of the theory describing Raman scattering from birefringent materials.
Design of a scanning laser optical trap for multiparticle manipulation
Authors: Mio C. , Gong T. , Terray A. , Marr D. W. M.
Published: July 2002

In recent years, single-beam optical traps have been used to manipulate individual colloids and biological objects such as cells. We have implemented a rapidly scanning laser optical trap with rates as high as 1200 Hz where a single laser beam is used to trap multiple colloids simultaneously. The optics are optimized to achieve a small laser focus size and a large scanning pattern in the sample. This approach provides great pattern flexibility and, because of the use of piezoelectrics, small particles (1 μm in diameter) in low-viscosity solvents, such as water, can be readily manipulated.
Indium phosphide passivation using thin layers of cadmium sulfide
Authors: Vaccaro K. , Dauplaise H. M. , Davis A. , Spaziani S. M. , Lorenzo J. P.
Published: July 2002

The electrical properties of the silicon dioxide/n-type (100) InP interface were significantly improved by thin interlayers of chemical bath deposited CdS. The CdS layer and CdS/InP interface were investigated with x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). XPS data showed reduction of native oxides and the prevention of subsequent substrate oxide growth following CdS layer deposition. PL spectra, measured between 1.0 and 1.3 μm, indicate a reduction in phosphorus vacancies. Metal–insulator–semiconductor (MIS) capacitors fabricated with CdS-treated InP substrates displayed interface-state densities below 1×1011 eV−1 cm−2 when determined from the difference between the high- and low-frequency capacitance data.
Activation energies of Si donors in GaN
Authors: Götz W. , Johnson N. M. , Chen C. , Liu H. , Kuo C. , Imler W.
Published: July 2002

The electronic properties of Si donors in heteroepitaxial layers of GaN were investigated. The n-type GaN layers were grown by metalorganic chemical vapor deposition and either intentionally doped with Si or unintentionally doped. The samples were evaluated by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy. For both types of samples the n-type conductivity was found to be dominated by a donor with an activation energy between 12 and 17 meV. This donor is attributed to Si atoms substituting for Ga in the GaN lattice (SiGa). The range of activation energies is due to different levels of donor concentrations and acceptor compensation in our samples. The assignment of a PL signature to a donor–acceptor pair recombination involving the Si donor level as the initial state of the radiative transition yields the position of the optical Si donor level in the GaN bandgap at ∼Ec–(22±4) meV. A deeper donor level is also present in our GaN material with an activation energy of ∼34 meV which is tentatively assigned to oxygen donors substituting for nitrogen (ON).
Highly efficient band-edge emission from InP quantum dots
Authors: Mićić Olga I. , Sprague Julian , Lu Zhenghao , Nozik Arthur J.
Published: July 2002

High quality InP quantum dots with diameters ranging from 25 to 45 Å, have been prepared; these quantum dots (QDs) show high quantum yields for band-edge photoluminescence (lowest energy HOMO-LUMO transition). The wavelength of the blue-shifted band-edge emission ranges from about 575 to 730 nm depending on QD size. The quantum yield for photoluminescence is 30% at 300 K and 60% at 10 K; the multiexponential decay of this emission exhibits lifetimes ranging from 5 to 50 ns. Deep red-shifted emission due to trapping of carriers in defect states on the QD surface which exhibits lifetimes above 500 ns, has been eliminated by treating the QDs with a dilute solution of HF or NH4F.
Charge trapping and device behavior in ferroelectric memories
Authors: Seager C. H. , McIntyre D. C. , Warren W. L. , Tuttle B. A.
Published: July 2002

The electric field emanating from the surface of a poled ferroelectric (FE) can control the conduction properties of an overlying semiconducting (SC) film; this combination of materials can thus serve as a nondestructive readout (NDRO), nonvolatile memory device. We have characterized prototypes of these devices which utilize semiconducting In2O3 deposited on thin film lead zirconate titanate and bulk BaTiO3 FEs. The remanent state SC resistance in thin film FE NDRO devices is often opposite to that predicted from the known direction of FE polarization. In these cases charge injected from the SC film into the FE and trapped near the interface appears to control the electric field at the SC/FE interface. By contrast, the response of SC films on bulk FEs is largely controlled by just the FE remanent polarization. The measured SC resistance values in the ‘‘up’’ and ‘‘down’’ polarization states can be fairly accurately predicted by calculating the accumulation and depletion charge densities from the measured carrier concentrations, mobilities, and FE hysteresis behavior. We also observe a correlation between charge trapping in bulk and thin film of NDRO memory devices and the presence or absence of temperature-bias–stress-induced voltage shifts (imprint) of the FE hysteresis curves. We suggest that the presence of near-interfacial traps in the FE controls both imprint and NDRO memory response.
Absolute pressure measurements on a nanosecond time scale using surface plasmons
Authors: Schilling A. , Yavaş O. , Bischof J. , Boneberg J. , Leiderer P.
Published: July 2002

Transient acoustic waves generated by laser-induced bubble formation at a liquid–solid interface are sensitively monitored using optically excited surface plasmons. This method enables the detection of both the compressive and tensile waves with high accuracy as demonstrated for the propagation and reflection of acoustic pulses at a quartz–water interface. Unique advantages of this new technique are the high sensitivity of 0.1–0.2 MPa that could be achieved for absolute pressure measurements on a nanosecond time scale and its ability to probe exact pulse profiles due to the localized probe depth of surface plasmons.
Raman scattering of alternating nanocrystalline silicon/amorphous silicon multilayers
Authors: Wu X. L. , Siu G. G. , Tong S. , Liu X. N. , Yan F. , Jiang S. S. , Zhang X. K. , Feng D.
Published: July 2002

Nanocrystallite size distribution and structural properties in alternating hydrogenated nanocrystalline silicon/amorphous silicon multilayers were investigated by means of Raman scattering. The obtained Raman spectra show a broad peak at ∼480 cm−1 from amorphous Si and some small peaks superposed on the broad peak. According to the positions of the crystallite peak, the mean crystallite size and volume fraction of the crystalline were calculated. Since these small peaks have strong size dependence of their relative intensities, an effect induced by the atomic vibrations from the near-surface region of nanocrystals is considered to be responsible for the modification of the vibrational properties and the stable photoluminescence from our samples.
Detection of combinative infrared absorption bands in thin silicon dioxide films
Authors: Han Sang M. , Aydil Eray S.
Published: July 2002

Multiple total internal reflection Fourier transform infrared spectroscopy is used to detect combinational phonon bands of SiO2 at 1645, 1852, and 2000 cm−1 in thin films produced by plasma enhanced chemical vapor deposition. The isotopic shifts of these bands in films deposited from SiH4/18O2 mixtures proved that combinations of SiO2 phonons give rise to the additional absorption peaks. Detection of these combinative phonon bands enables one to use Si multiple total internal reflection crystals for studying Si–O phonon absorptions in SiO2 films on Si. In principle, films as thin as a few angstroms can be detected using the infrared absorption by the combinational bands.
“Blue” temperature-induced shift and band-tail emission in InGaN-based light sources
Authors: Eliseev Petr G. , Perlin Piotr , Lee Jinhyun , Osiński Marek
Published: July 2002

Electro- and photoluminescence spectra of high-brightness light-emitting AlGaN/InGaN/GaN single-quantum-well structures are studied over a broad range of temperatures and pumping levels. Blue shift of the spectral peak position was observed along with an increase of temperature and current. An involvement of band-tail states in the radiative recombination was considered, and a quantitative description of the blue temperature-induced shift was proposed assuming a Gaussian shape of the band tail.
Experimental quasiparticle dynamics in a superconducting, imaging x-ray spectrometer
Authors: Friedrich S. , Segall K. , Gaidis M. C. , Wilson C. M. , Prober D. E. , Szymkowiak A. E. , Moseley S. H.
Published: July 2002

We present an experimental study of the time scales for various quasiparticle processes in a superconducting single photon spectrometer. Processes studied include quasiparticle recombination, diffusion, trapping, tunneling, and energy redistribution. Experiments were performed with a double junction, imaging x-ray detector whose charge output provides a measure of the photon energy. Time scales are extracted with a simple model and the values of several parameters, including the diffusion constant and recombination time, are found to differ from theoretical predictions. These results provide guidelines for performance analysis, device scaling, and future designs.
Junction devices based on sulfonated polyaniline
Authors: Narasimhan M. , Hagler M. , Cammarata V. , Thakur M.
Published: July 2002

Schottky diodes were fabricated using aluminum/neutralized-sulfonated-polyaniline (SPAN) junctions. I–V and C–V measurements were made, and the barrier height (ΦB) and the background concentration (NB) were determined to be 0.8 V and 4×1017/cm3, respectively. Using these diodes as gate control, depletion-mode thin-film transistors were fabricated with a source and drain made of gold Ohmic contacts. The transistors were characterized by I–V measurements, and the carrier mobility determined from devices operating in the |VG|>|VDS| “linear” regime was about 0.01 cm2/V s. This high value of mobility could be attributed to the spherulitic (partially ordered) structures observed in the SPAN thin films. Field-effect transistors were also fabricated on SPAN films deposited on an n-doped silicon substrate acting as the gate electrode with a thermally grown oxide layer. A reasonably high on/off ratio (∼4×103) was measured in these devices.