bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of proto‐oncogenic and mutant forms of the transmembrane region of the Neu receptor in TFE
Authors: Houliston R.Scott , Hodges Robert S. , Sharom Frances J. , Davis James H.
Published: January 2003

A single mutation within the transmembrane region of the Neu receptor (Val664→Glu) is known to enhance tyrosine kinase activity, by promoting receptor dimerization. In order to gain insight into potential structural changes that arise as a result of the mutation, peptides corresponding to the complete transmembrane domain of proto‐oncogenic and mutant forms of Neu have been studied by 1H nuclear magnetic resonance in the solvent trifluoroethanol (TFE). The chemical shifts are similar for both forms of the peptide, with the exception of amide residues close to the mutation site. Both peptides adopt a helical conformation, with a distinct bend one turn downstream of the mutation site. This deformation gives rise to several nuclear Overhauser effects, the majority of which were detected in both peptides, that are atypical for a straight canonical α‐helix. Our data in this solvent do not support a conformational change in the transmembrane domain of monomeric Neu as a result of the mutation. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis indicates that proto‐oncogenic Neu peptides have a higher propensity to oligomerize in the solvent TFE than the Glu664 oncogenic form.
Identification and characterization of Mlr1,2: two mouse homologues of Mblk‐1, a transcription factor from the honeybee brain
Authors: Kunieda Takekazu , Park Jung-Min , Takeuchi Hideaki , Kubo Takeo
Published: January 2003

We previously identified the Mblk‐1 gene in the honeybee brain, which encodes a transcription factor containing two DNA binding motifs, termed RHF1 and 2 (Takeuchi et al. (2001) Insect Mol. Biol. 121, 134–140). Here, we identified two mouse Mblk1 homologues, Mlr1 and Mlr2. Both encode proteins containing a single DNA‐binding motif highly conserved with RHF2 and activate transcription mediated by a DNA element recognized by honeybee Mblk‐1. Mlr1 was expressed predominantly in the spermatocytes of the testis, while Mlr2 was expressed in various tissues other than testis. Mlr1 transcripts were lost in the testis of W/Wv
mutant mice, suggesting a role in spermatogenesis.
Ezrin is a substrate for Lck in T cells
Authors: Autero Matti , Heiska Leena , Rönnstrand Lars , Vaheri Antti , Gahmberg Carl G , Carpén Olli
Published: January 2003

We evaluated the role of Lck tyrosine kinase, an early effector of T cell activation, in regulation of the membrane–cytoskeleton linker protein ezrin. Ezrin was constitutively tyrosine phosphorylated in wild‐type and CD45‐deficient Jurkat T cells, but not in Lck‐deficient cells. However, phosphorylation was evident in cells, in which Lck activity had been restored by transfection. Phosphorylation was reduced by the Src family kinase inhibitor PP2 and increased by the tyrosine phosphatase inhibitor pervanadate, implying continuous tyrosine phosphorylation and dephosphorylation. Lck phosphorylated ezrin in vitro, and the major phosphotyrosine was identified as Y145. These results identify ezrin as the first cytoskeletal substrate for Lck.
Modulation of EGF receptor autophosphorylation by α‐hemolysin of Staphylococcus aureus via protein tyrosine phosphatase
Authors: Vandana Sharma , Navneet Sangha , Surinder Kaur , Krishnasastry M.V
Published: January 2003

In the presence of assembled α‐hemolysin (α‐HL) of Staphylococcus aureus, the epidermal growth factor receptor (EGFr) is rapidly dephosphorylated. Several obvious possibilities that otherwise would have contributed to the dephosphorylation were ruled out. Instead, an elevation in the activity of a protein tyrosine phosphatase appears to be responsible for the observed loss of phosphorylation signal of EGFr. For this dephosphorylation, the assembly of α‐HL is necessary while lytic pore formation is not required. In summary, the EGFr is unable to retain its phosphorylation signal in the presence of α‐HL and the process is irreversible.
Sphingosine‐1‐phosphate stimulates cortisol secretion
Authors: Rábano Miriam , Peña Ana , Brizuela Leyre , Marino Aida , Macarulla José Marı́a , Trueba Miguel , Gómez-Muñoz Antonio
Published: January 2003

We show here for the first time that sphingosine‐1‐phosphate (Sph‐1‐P) stimulates cortisol secretion in zona fasciculata cells of bovine adrenal glands. This effect was dependent upon protein kinase C (PKC) and extracellular Ca2+, and was inhibited by pertussis toxin. Sph‐1‐P activated phospholipase D (PLD) through a pertussis toxin‐sensitive mechanism, also involving extracellular Ca2+ and PKC. Primary alcohols, which attenuate formation of phosphatidic acid (the product of PLD), and cell‐permeable ceramides, which inhibit PLD, blocked Sph‐1‐P‐induced cortisol secretion. In conclusion, Sph‐1‐P stimulates cortisol secretion through a mechanism involving Gi/o protein‐coupled receptors, extracellular Ca2+, PKC and PLD.
Stress‐induced hyperphosphorylation of tau in the mouse brain
Authors: Okawa Yasuhiro , Ishiguro Koichi , Fujita Shinobu C
Published: January 2003

We previously showed that starvation causes reversible hyperphosphorylation of tau in the mouse brain. To explore possible involvement of stress in tau hyperphosphorylation quantitative analysis of phosphorylated tau in four brain regions of mice subjected to cold water stress (CWS) was made by immunoblot analyses using phosphorylation‐dependent antibodies directed to eight sites on tau known to be hyperphosphorylated in the brain of Alzheimer's disease (AD) patients. Ser199, Ser202/Thr205, Thr231/Ser235 were hyperphosphorylated 20 and 40 min after CWS. The response was pronounced in the hippocampus and cerebral hemisphere, but weak in the cerebellum in parallel with the regional vulnerability in AD. Among the regulatory phosphorylation of protein kinases studied, a transient phosphorylation of tau protein kinase I/glycogen synthase kinase 3β at Ser9 was most conspicuous.
Enhancement of TNF‐α‐mediated cell death in vascular smooth muscle cells through cytochrome c‐independent pathway by the proteasome inhibitor
Authors: Kim Hak Hyung , Kim Koanhoi
Published: January 2003

There is substantial evidence that cytokines induce apoptosis of vascular smooth muscle cells (VSMCs) in atherosclerosis. Its regulation, however, is not completely defined. The aim of this study is to investigate whether proteasome activity is related with apoptosis in VSMCs by tumor necrosis factor‐α (TNF‐α). Rat aorta smooth muscle cells were treated with TNF‐α and proteasome inhibitor MG132 and then cell death was determined by morphology, viability, and DNA fragmentation. MG132 or TNF‐α alone did not induce cell death. In contrast, co‐treatment of TNF‐α and proteasome inhibitor induced death and DNA degradation in VSMCs, suggesting proteasome inhibitor enhanced death activity of TNF‐α. The death was not blocked by ascorbic acid but by nitric oxide synthase inhibitor N
G‐monomethyl‐L‐arginine. Both caspase‐3 and ‐8 were activated during the death by the proteasome inhibitor and TNF‐α. The death was effectively blocked by the caspase‐3 inhibitor z‐DEVD‐fmk, suggesting a role of caspase‐3 in the death. Nonetheless, there were no significant alterations in the level of Bcl‐2, Bcl‐XL, Bax and Bak by the proteasome inhibitor, nor any evidence of cytochrome (cyt) c release into cytosol from dying cells, suggesting that cyt c is not involved. These results suggest that proteasome inhibition potentiates TNF‐mediated death in VSMCs in a cyt c‐independent pathway. The present study proposes a new mechanism by which VSMCs undergo death by cytokines.
Escaping or connecting? Characteristics of youth who form close online relationships
Authors: Wolak Janis , Mitchell Kimberly J , Finkelhor David
Published: January 2003

We used data from a US national sample of Internet users, ages 10–17 (N=1501), to explore the characteristics of youth who had formed close relationships with people they met on the Internet (n=210). Girls who had high levels of conflict with parents or were highly troubled were more likely than other girls to have close online relationships, as were boys who had low levels of communication with parents or were highly troubled, compared to other boys. Age, race and aspects of Internet use were also related. We know little about the nature or quality of the close online relationships, but youth with these sorts of problems may be more vulnerable to online exploitation and to other possible ill effects of online relationships. At the same time, these relationships may have helpful aspects.
Illicit drug use, cigarette smoking and alcohol drinking behaviour among a sample of high school adolescents in the Pietersburg area of the Northern Province, South Africa
Authors: Madu Sylvester Ntomchukwu , Matla Ma‐Queen Patience
Published: January 2003

Aim

The aim of this study was to investigate the prevalence of illicit drug use, cigarette smoking and alcohol drinking behaviour among a sample of high‐school adolescents in the Pietersburg area (Central Region) of the Northern Province, South Africa.

Participants

Participants in this study were 435 secondary‐school adolescent students around the Pietersburg area (Central Region), in the Northern Province. Two hundred and forty‐three (56%) participants were female and 192 (44%) were male. They were aged between 15 and 19 years, with the mean age of 17.25 years (s.d.=1.34). Their educational level ranged between standards 7 and 10 (Grades 9–12).

Instruments

Participants’ demographic variables were determined by use of a questionnaire which covered participants personal characteristics such as age and gender, as well as educational level. Illicit drug use, cigarette smoking, and alcohol drinking behaviour were also measured using the questionnaire.

Results

Findings of this study indicate the prevalence rate of 19.8% for illicit drug use, 10.6% for cigarette smoking and 39.1% for alcohol consumption among the participants. Both drug use, cigarette smoking and alcohol consumption are associated more with males than with females. The majority of the drug users and cigarette smokers indicated that they do so when they are bored, tired or stressed up, or at parties; and most of those who drink alcohol indicated that they do so at parties, weekends, or any other time. The mean age for first drug use is 14.9 years (s.d.=1.77); 14.54 years (s.d.=1.80) for first cigarette smoking and 15.33 years (s.d.=1.91) for first alcohol consumption. Among those who drink alcohol, 24.1% and 14.1% experience unplanned drunkenness and irritability, respectively. Unplanned drunkenness is associated with males, while unplanned irritability (after drinking alcohol) is not associated with any gender.

Conclusion

Mental health workers and the law‐enforcement agencies should take note of the above findings while planning preventive and therapeutic strategies for the reduction of drug use, cigarette smoking and alcohol use and abuse among adolescents in the area.
No relationship between testosterone levels and depressive symptoms in aging men
Authors: Kaneda Yasuhiro , Fujii Akira
Published: January 2003

We investigated the associations between depression and serum testosterone levels in the elderly. There was no significant difference in the mean levels of the serum testosterone between the groups of patients and normals. For both groups, there was no significant correlation between testosterone and total depression scores or age.
Antiepileptic drugs in schizophrenia: a review
Authors: Hosák L. , Libiger J.
Published: January 2003

The first choice group of psychotropic agents in schizophrenia is neuroleptics. However, this treatment is not effective in all patients and with every symptom. We summarize papers published on the role of antiepileptic drugs in treatment-resistant schizophrenia. We have searched the computer database system MEDLINE for relevant articles including reviews, reports of drug studies and case histories. Antiepileptic drugs can change symptoms of schizophrenia by their action on GABA-ergic neurotransmission or via anti-glutamatergic mechanisms. High doses of adjunctive benzodiazepines reduce positive symptoms, anxiety, and agitation. Carbamazepine is effective in affective symptoms of schizophrenia and influences violent behavior in psychotic patients. Its anti-kindling action may represent a promising treatment strategy for some patients with chronic course of schizophrenia. Valproate treatment leads to a decrease in positive symptoms as well as hostility. Lamotrigine is expected to influence the positive, negative, affective, and cognitive symptoms of schizophrenia. New antiepileptics (e.g., gabapentin, oxcarbazepine, topiramate, vigabatrin) present a promise as potential adjuncts to neuroleptic treatment in resistant symptoms of schizophrenia.
Transmitral pulsed‐Doppler echocardiography is a more accurate technique compared with two‐dimensional echocardiography using dobutamine, in patients with one vessel coronary artery disease
Authors: Bajraktari Gani , Qirko Spiro , Fusco Rossana , Milazzo Angela , Xhaxho Brunilda , Pezzano Antonio
Published: January 2003

To examine the effects of dobutamine on pulsed‐Doppler left ventricular filling indices and its utility for evaluation of CAD we studied 14 patients with normal coronary arteries (Group 1) and 39 patients with significant CAD (>70% diameter stenosis). Patients with coronary artery disease (CAD) were divided into two groups: patients with one‐vessel coronary disease (Group 2); and those with multivessel CAD (Group 3). After stopping cardioactive treatment, patients underwent incremental dobutamine stress (5, 10, 20, 30 and 40 μg/kg/min) during pulsed‐Doppler interrogation of diastolic filling with simultaneous heart rate and blood pressure measurements. The following transmitral Doppler variables were measured at baseline and at peak‐dose of dobutamine: peak early (E) and peak atrial (A) velocity; E/A ratio; acceleration time (AT) and deceleration time (DT) of E wave; isovolumic relaxation time (IVRT); and time–velocity integral (TVI). Two‐dimensional echocardiography was performed to detect regional asinergy and analyzed using a 16 segment model. Results: Normals and CAD patients showed comparable changes in heart rate and blood pressure (P=NS between groups). Intergroup analysis of the changes of transmitral flow showed the significant changes for these indices (P<0.001): E velocity (−2.78±10.04, 12.4±9.4 and 16.47±10.65 cm/s); AT of E wave (1.66±2.47, −5.2±1.38 and −4.66±2.39 m/s2); DT of E wave (−0.23±0.18, 0.2±0.2 and 0.2±0.28 m/s2); and TVI of transmitral flow (−1.26±0.7, 3.5±1.75 and 4.1±1.66 cm), respectively for Groups 1, 2 and 3. All other transmitral Doppler variables showed insignificant changes (P=NS) to dobutamine between groups. It is important that the significance of these changes were the same for patients with one‐vessel and those with multivessel coronary disease. In conclusion, during dobutamine stress testing, patients with CAD, had an abnormal response of these transmitral Doppler indices: E wave; AT of E wave; DT of E wave; and the TVI of transmitral flow. The abnormal responses of these Doppler indices of left ventricular filling are more accurate markers of significant single vessel CAD than new wall motion abnormalities during conventional DSE.
Effect of early revascularisation in cardiogenic shock complicating acute myocardial infarction. A single center experience
Authors: Lindholm M.G. , Aldershvile J. , Sundgreen C. , Jørgensen Erik , Saunamäki Kari , Boesgaard S.
Published: January 2003

Background:

Five to 10% of patients with acute myocardial infarction develop cardiogenic shock and the majority of these patients are expected to die within the first few weeks. In this study, we review our recent experience in the management of patients with cardiogenic shock complicating MI and examine the effect of early invasive revascularisation on mortality.

Methods:

Thirty‐six consecutive patients who developed cardiogenic shock less than 48 h after MI were retrospectively evaluated and divided into two treatment groups. One group received early invasive revascularisation (n=24) and the other group had no early invasive revascularisation, but received similar conventional intensive care medical treatment (n=12).

Results:

Baseline characteristics and hemodynamic variables were similar in both groups. Apart from invasive revascularisation and the use of intra aortic balloon counterpulsation (IABP), treatment strategies did not differ between the two groups. Thirty‐day mortality was 21% in the revascularised group of patients and 58% in the non‐revascularised group (P<0.05).

Conclusions:

Our data support previous observations suggesting that an aggressive treatment strategy including early invasive revascularisation and IABP is associated with improved short and long‐term survival in patients with cardiogenic shock. Since early revascularisation appears safe with a considerable treatment benefit, this approach must be considered in patients with short shock duration early after MI.
Spectrometry of charged particles from inertial-confinement-fusion plasmas
Authors: Séguin F. H. , Frenje J. A. , Li C. K. , Hicks D. G. , Kurebayashi S. , Rygg J. R. , Schwartz B.-E. , Petrasso R. D. , Roberts S. , Soures J. M. , Meyerhofer D. D. , Sangster T. C. , Knauer J. P. , Sorce C. , Glebov V. Yu. , Stoeckl C. , Phillips T. W. , Leeper R. J. , Fletcher K. , Padalino S.
Published: January 2003

High-resolution spectrometry of charged particles from inertial-confinement-fusion (ICF) experiments has become an important method of studying plasma conditions in laser-compressed capsules. In experiments at the 60-beam OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)], utilizing capsules with D2, D3He, DT, or DTH fuel in a shell of plastic, glass, or D2 ice, we now routinely make spectral measurements of primary fusion products (p, D, T, He3, α), secondary fusion products (p), “knock-on” particles (p, D, T) elastically scattered by primary neutrons, and ions from the shell. Use is made of several types of spectrometers that rely on detection and identification of particles with CR-39 nuclear track detectors in conjunction with magnets and/or special ranging filters. CR-39 is especially useful because of its insensitivity to electromagnetic noise and its ability to distinguish the types and energies of individual particles, as illustrated here by detailed calibrations of its response to 0.1–13.8 MeV protons from a Van de Graaff accelerator and to p, D, T, and α from ICF experiments at OMEGA. A description of the spectrometers is accompanied by illustrations of their operating principles using data from OMEGA. Sample results and discussions illustrate the relationship of secondary-proton and knock-on spectra to capsule fuel and shell areal densities and radial compression ratios; the relationship of different primary fusion products to each other and to ion temperatures; the relationship of deviations from spherical symmetry in particle yields and energies to capsule structure; the acceleration of fusion products and the spectra of ions from the shell due to external fields; and other important physical characteristics of the laser-compressed capsules.
Understanding congruent melting in binary solids: Molecular models of benzene–hexafluorobenzene mixtures
Authors: Schroer J. W. , Monson P. A.
Published: January 2003

We present a Monte Carlo computer simulation study of solid–fluid and solid–solid equilibrium in molecular models representative of binary mixtures of benzene and hexafluorobenzene. The models considered treat the molecular shape with hard sphere interaction site potentials and the electrostatic interactions via quadrupole–quadrupole potentials. Monte Carlo simulations are used to calculate the free energy of the pure solids and the 1:1 solid compound that appear in the phase diagram, and also the solution thermodynamics in the fluid phase. In common with the real fluid phase mixtures of benzene and hexafluorobenzene the fluid phase of the model is close to an ideal mixture. The model also exhibits solid–fluid and solid–solid equilibrium similar to that seen experimentally.The results indicate that enhanced stability of the benzene-hexafluorobenzene 1:1 solid compound can be understood in terms of the cooperative effects of electrostatic interactions and the packing of the anisotropic repulsive cores of the molecules.
Verification of the vibrational exciton approach for CO2 and N2O nanoparticles
Authors: Signorell Ruth
Published: January 2003

It is investigated how far the vibrational exciton approximation is suitable to describe the characteristic band shapes in the infrared spectra of CO2 and N2O nanoparticles. The particles typically contain between 50 and 104 molecules and have spatial dimensions between 1 and 10 nm. The accuracy of the exciton approach is estimated by comparison with experimental data and quantum chemical calculations for small clusters. The spectral changes due to different particle shapes and particle sizes are investigated with respect to the estimated accuracy. This includes the determination of a typical effective range for the dipole–dipole coupling.
Development of an electrostatic levitator for neutron diffraction structure analysis
Authors: Aoki Hirokatsu , Paradis Paul-François , Ishikawa Takehiko , Aoyama Tomotsugu , Masaki Tadahiko , Yoda Shinich , Ishii Yoshinobu , Itami Toshio
Published: January 2003

An electrostatic levitation (ESL) furnace was designed for the neutron diffraction study of condensed matter. This apparatus is composed of an electrostatic levitator, a neutron inlet path with Cd slit, a 160 degree window for the scattered neutrons, a CO2 laser for sample heating, and an optical pyrometer for temperature measurements. A preliminary neutron diffraction experiment with this ESL was performed for polycrystalline alumina. The sample position could be controlled with an accuracy of ±0.1 mm. The observed Bragg peaks were in complete agreement with those derived from the lattice data of alumina obtained from the literature value. This indicates that this facility is attractive for the structural study of condensed matter without containers.
A microcontroller-based failsafe for single photon counting modules
Authors: Gordon Matthew P. , Selvin Paul R.
Published: January 2003

Avalanche photodiode-based single photon counting modules (SPCMs) can be damaged by exposure to excessive light levels. A flexible and inexpensive failsafe is presented which has been shown to protect SPCMs from light levels far exceeding the damage threshold.
Low noise, low power consumption high electron mobility transistors amplifier, for temperatures below 1 K
Authors: Oukhanski N. , Grajcar M. , Il’ichev E. , Meyer H.-G.
Published: January 2003

Low noise three-stage pseudomorphic high electron mobility field-effect transistors amplifier were designed for the temperature range below 1 K. A minimum noise temperature TN≈100 mK was measured at an ambient temperature of about 380 mK at frequencies between 1 and 4 MHz for a source resistance of 10 kΩ. The gain of the amplifier was 50 at a power consumption of about 200 μW. The noise parameters of the amplifier are stable to within 30%, for a power consumption in the range of 100–300 μW. Minimum voltage spectral noise density of the amplifier with respect to the input is about 200 pV/Hz1/2 and the corner frequency of the 1/f noise is close to 300 kHz.
Noncontact technique for determining the thermal diffusivity coefficient on acoustically levitated liquid drops
Authors: Ohsaka K. , Rednikov A. , Sadhal S. S.
Published: January 2003

We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids, which exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in a flattened drop shape using an acoustic levitator and heating it with a laser beam. The heated drop is then subjected to natural cooling by heat loss from the surface. Due to acoustic streaming, the heat loss mainly occurs through the equator section of the drop. The measured cooling rate in combination with a radial heat conduction model allows us to calculate the thermal diffusivity coefficient of the drop. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. The technique is well suited if the thermal diffusivity coefficient of the liquid in the normal state (i.e., above the freezing point) is known or can be measured by conventional techniques.
Optimization of a focusing monochromator
Authors: Mergia K. , Messoloras S.
Published: January 2003

The procedure for optimizing the performance of a focusing monochromator using a linear position sensitive detector is described. Analytical expressions describing the reflected beam profile are derived. The methodology for deriving the calibration function of the focusing device and its application to different Bragg reflections is discussed. The optimum conditions for a given sample height in order to attain either homogeneous beam or a maximum reflected intensity are presented.
Spatial characterization of extreme ultraviolet plasmas generated by laser excitation of xenon gas targets
Authors: Kranzusch Sebastian , Peth Christian , Mann Klaus
Published: January 2003

At Laser-Laboratorium Göttingen laser-plasma sources were tested, which are going to be used for characterization of optical components and sensoric devices in the wavelength region from 11 to 13 nm. In all cases extreme ultraviolet (EUV) radiation is generated by focusing a Q-switched Nd:YAG laser into a pulsed gas puff target. By the use of xenon or oxygen as target gas, broadband as well as narrowband EUV radiation is obtained, respectively. Different types of valves and nozzles were tested in order to optimize the emitted radiation with respect to maximum EUV intensities, small source diameters, and positional stability. The investigation of these crucial source parameters was performed with specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows both spatially and angular resolved monitoring of the soft x-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found. The data were compared with fluorescence measurements for visualization of the target gas jet. The experimental observations can be explained by reabsorption of the generated EUV radiation in the surrounding target gas, as supported by semiempirical model calculations based on the attenuation in the three-dimensional gas density according to Lambert–Beer’s law. As a consequence of the presented investigations, an optimization of the EUV source with respect to intensity, plasma shape, and angular dependence is achieved, resulting in a spherical plasma of 200 μm diameter and a 50% increase of the EUV pulse energy.
Piezoelectric droplet ejector for ink-jet printing of fluids and solid particles
Authors: Perçin Gökhan , Khuri-Yakub Butrus T.
Published: January 2003

In this article, we present a technique for the deposition of inks, organic polymers, and solid particles, using a fluid ejector. The ejector design is based on a flextensional transducer that excites axisymmetric resonant modes in a clamped circular plate. It is constructed by bonding a thin piezoelectric annular disk to a thin edge clamped circular plate. Liquids or solid particles are placed behind one face of the plate which has a small orifice (50–200 μm diameter) at its center. By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejection of photoresist (Shipley Microposit S1400-21, S1400-27, S1805, and S1813), oil-based ink, water, or talcum powder [Mg3Si4O10(OH)2] has been achieved. Successful deposition of a photoresist has been accomplished without spinning, and thus without waste. A boundary integral method was used to numerically simulate drop formation from the vibrating orifice. Simulations have been used to optimize ejection performance.
A low-temperature ultrahigh vacuum atomic force microscope for biological applications
Authors: Radenović Alexandra , Bystrenová Eva , Libioulle Laurent , Taborelli Mauro , DeRose James A. , Dietler Giovanni
Published: January 2003

We present an atomic force microscope (AFM) for operation at low temperatures under ultrahigh vacuum conditions. It uses the laser beam deflection method to measure the bending of the cantilever. The four quadrant photodiode allows the detection of vertical and lateral forces. The AFM has been developed for studying biological samples. Images of deoxyribonucleic acid plasmids have been obtained in contact mode.
Performance of laminar-type holographic grating for a soft x-ray flat-field spectrograph in the 0.7–6 nm region
Authors: Koike Masato , Sano Kazuo , Gullikson Eric , Harada Yoshihisa , Kumata Hideki
Published: January 2003

A laminar-type holographic grating having a groove density of 2400 lines/mm was designed and fabricated for use with a soft x-ray flat-field spectrograph covering the 0.7–6 nm region. The varied-line-spaced grating pattern was generated by use of an aspheric wave front recording system and the laminar-type grooves were formed by a reactive ion-etching method. The performance of the grating was evaluated by using a molybdenum K x-ray generator and a spectrograph with a charge coupled device imaging detector. Also, the absolute diffraction efficiencies of the zeroth, first, second, and third, spectral orders were measured by use of the reflectometers installed at Synchrotron Radiation Beamlines. The experimental results showed that the holographic grating indicated comparable spectral resolution and maximum first-order diffraction efficiency (>2%) at ∼2 nm with a replica grating made from a mechanically ruled varied-line-spacing grating. It also showed higher efficiency in the <1.0 nm region and lower level higher-order light over the whole wavelength range than the replica grating.
Low noise current-to-voltage converter and vibration damping system for a low-temperature ultrahigh vacuum scanning tunneling microscope
Authors: Libioulle Laurent , Radenovic Alexandra , Bystrenova Eva , Dietler Giovanni
Published: January 2003

The design of low-temperature tunnel current converters and the design of a low-temperature damping stage for a scanning tunneling microscope (STM) are presented. The current amplifiers are able to measure very low tunnel current (down to 0.25 pA), while preserving a sufficient bandwidth for topographic and spectroscopic measurements and with very low noise characteristics (down to 3 fA Hz−1/2). The design of a compact low-temperature magnetic damping stage with a resonance frequency of about 7 Hz, protecting the microscope mechanics against mechanical vibrations of the cryostat is also described. The damped stage with the microscope mechanics is in contact with the cryostat during cooling, while during the STM measurements, it is mechanically isolated.
A laboratory apparatus for the measurement of optical extinction coefficients of postflame soot in the infrared
Authors: Widmann John F. , Yang Jiann C. , Bundy Matthew , Tsai Benjamin K. , Mulholland George W.
Published: January 2003

An experimental apparatus for the measurement of optical extinction coefficients of postflame soot aerosol in the infrared region of the electromagnetic spectrum is presented. Reproducible soot aerosol is generated using a laminar diffusion burner, and the mass concentration of the aerosol is determined gravimetrically. The instrument, which utilizes an infrared spectrograph for the extinction measurements, provides data over the wavelength range 2.5–5.0 μm. The infrared spectrograph, which provides a near-instantaneous measurement of the incident radiation over a range of wavelengths, is ideal for applications in which the deposition of soot over time on the optical windows can interfere with the measurement. Furthermore, the wavelength dependence of the extinction coefficient can be determined independently of the gravimetric measurements, which represents the dominant source of uncertainty in the measurement of the mass specific extinction coefficient. The spectrograph reported herein has been characterized using a well-characterized sodium heat pipe blackbody, and the responsivity of the instrument has been quantified as a function of wavelength.
A paralleled readout system for an electrical DNA-hybridization assay based on a microstructured electrode array
Authors: Urban Matthias , Möller Robert , Fritzsche Wolfgang
Published: January 2003

DNA analytics is a growing field based on the increasing knowledge about the genome with special implications for the understanding of molecular bases for diseases. Driven by the need for cost-effective and high-throughput methods for molecular detection, DNA chips are an interesting alternative to more traditional analytical methods in this field. The standard readout principle for DNA chips is fluorescence based. Fluorescence is highly sensitive and broadly established, but shows limitations regarding quantification (due to signal and/or dye instability) and the need for sophisticated (and therefore high-cost) equipment. This article introduces a readout system for an alternative detection scheme based on electrical detection of nanoparticle-labeled DNA. If labeled DNA is present in the analyte solution, it will bind on complementary capture DNA immobilized in a microelectrode gap. A subsequent metal enhancement step leads to a deposition of conductive material on the nanoparticles, and finally an electrical contact between the electrodes. This detection scheme offers the potential for a simple (low-cost as well as robust) and highly miniaturizable method, which could be well-suited for point-of-care applications in the context of lab-on-a-chip technologies. The demonstrated apparatus allows a parallel readout of an entire array of microstructured measurement sites. The readout is combined with data-processing by an embedded personal computer, resulting in an autonomous instrument that measures and presents the results. The design and realization of such a system is described, and first measurements are presented.
Plasma interferometry at high pressures
Authors: Akhtar Kamran , Scharer John E. , Tysk Shane M. , Kho Enny
Published: January 2003

A general formulation for the measurement of plasma density and effective collision frequency for lowly as well as highly, collisional plasmas using millimeter wave interferometry is presented. In the presence of high density and collisionality at high gas pressures where the collision frequency (ν) is of the order of both the plasma (ωp) and the wave frequency of the millimeter wave (ω) (ν∼ω,ωp), the measured line-average plasma density has a complex dependence on phase shift as well as the amplitude change of the millimeter wave signal. The measurement scheme and analysis presented in this article show that for collisional plasmas, simultaneous measurement of the phase change and the amplitude change data is required to uniquely determine the plasma density and collision frequency. The treatment allows the application of millimeter wave interferometry to a wide range of relative collision frequency, wave frequency and plasma frequency since it uniquely determines the line-average plasma density and effective collision frequency using the phase and amplitude change data. This diagnostic is particularly valuable at plasma densities (ne<1014/cm3) and high pressures (P>10 Torr) where Langmuir probe and optical emission diagnostics including the Stark effect are not accurate for density measurements.
Clipping the tail of a TE–CO2 laser pulse using a gas breakdown technique for high resolution chemical plume detection
Authors: Bellecci Carlo , Bellucci Ida , Gaudio Pasqualino , Martellucci Sergio , Petrocelli Giovanni , Richetta Maria
Published: January 2003

In this article we present the realization of a spark-induced plasma shutter, working in free atmosphere, to clip off the nitrogen tail of a TE CO2 laser source. The clipping mechanism has been tested and gain switched spike pulses ranging between 100 and 115 ns have been obtained at 10P20-laser line. The shutter mechanism was optimized. In this way a clipping efficiency of 100% and a jitter value around 15 ns were obtained.
The Xe129 nuclear shielding tensor surfaces for Xe interacting with rare gas atoms
Authors: Jameson Cynthia J. , Sears Devin N. , de Dios Angel C.
Published: January 2003

The shielding tensor surfaces for the Xe–Xe, Xe–Kr, Xe–Ar, and Xe–Ne dimers are calculated as a function of separation, using gauge-including atomic orbitals (GIAO) at the Hartree–Fock level, and also using density functional theory with the B3LYP hybrid functional. Since the highest quality potential energy functions are available for these systems, the available experimental data (temperature dependent second virial coefficients of the nuclear magnetic resonance chemical shifts) are from measurements on well-defined physical systems (Xe at low mole fraction in the gas phase), and the relation between the observed quantity and the shielding function is well-defined, these systems provide a means by which the dispersion component of the isotropic shielding function of Xe–Rg can be determined. The parallel component of the intermolecular shielding tensor is small and nearly independent of the method of calculation. Therefore, the dispersion component of the perpendicular component of the shielding function can be determined.
Dynamics of Cr(CO)6+ collisions with hydrogenated surfaces
Authors: Song Kihyung , Meroueh Oussama , Hase William L.
Published: January 2003

Classical trajectory simulations are used to study the activation of Cr(CO)6+ ions by 5–110 eV collisions with n-hexyl thiolate self-assembled monolayer (SAM) and the H-terminated diamond {111} surfaces. The transfer of the ion’s initial translational energy Ei to the ion’s internal degrees of freedom Eint, to the surface Esurf, and to final translational energy Ef depends on both Ei and the surface. At Ei=70 eV the percent energy transfers to Eint, Esurf, and Ef are 9, 81, and 10 for collision with the SAM and 17, 29, and 54 for collision with diamond. For collision with the SAM, the percent energy transfer to Eint is 8–10% and nearly independent of Ei, while it depends on Ei for collision with diamond. The percent transfer to Eint, for collision with the SAM, is in excellent agreement with experiment. For both surfaces, the percent energy transfer to Esurf and to Ef increase and decrease, respectively, as Ei is increased. For Ei of 30 and 70 eV the Cr(CO)n+, n=4–6, ions shatter as Cr(CO)6+ strikes the diamond surface. At 110 eV some of the n=1–3 ions also begin to shatter. Shattering is only observed for collision with the SAM at an Ei of 110 eV, for which the n=4–6 ions shatter. At lower Ei, the Cr(CO)6+ ions rebound off the SAM and dissociate via intramolecular vibrational energy redistribution, with lifetimes approximately the same as those of Rice–Ramsperger–Kassel–Marcus theory. Energy partitioning to the Cr(CO)n+→Cr(CO)n−1++CO, n=1–6, dissociation products is nonstatistical, with the partitioning to relative translation and CO vibrational and rotational energy, larger and smaller, respectively, than the prediction of phase space theory. There is negligible energy transfer to the CO vibration during the collision of Cr(CO)6+ with either surface or later as a result of intramolecular vibrational energy redistribution after the Cr(CO)n+ ions scatter off the surfaces.
Algorithms and novel applications based on the isokinetic ensemble. II. Ab initio molecular dynamics
Authors: Minary Peter , Martyna Glenn J. , Tuckerman Mark E.
Published: January 2003

In this paper (Paper II), the isokinetic dynamics scheme described in Paper I is combined with the plane-wave based Car–Parrinello (CP) ab initio molecular dynamics (MD) method [R. Car and M. Parrinello, Phys. Rev. Lett. 55, 2471 (1985)] to enable the efficient study of chemical reactions and metallic systems. The Car–Parrinello approach employs “on the fly” electronic structure calculations as a means of generating accurate internuclear forces for use in a molecular dynamics simulation. This is accomplished by the introduction of an extended Lagrangian that contains the electronic orbitals as fictitious dynamical variables (often expressed directly in terms of the expansion coefficients of the orbitals in a particular basis set). Thus, rather than quench the expansion coefficients to obtain the ground state energy and nuclear forces at every time step, the orbitals are “propagated” under conditions that allow them to fluctuate rapidly around their global minimum and, hence, generate an accurate approximation to the nuclear forces as the simulation proceeds. Indeed, the CP technique requires the dynamics of the orbitals to be both fast compared to the nuclear degrees of freedom while keeping the fictitious kinetic energy that allows them to be propagated dynamically as small as possible. While these conditions can be easy to achieve in many types of systems, in metals and highly exothermic chemical reactions difficulties arise. (Note, the CP dynamics of metals is incorrect because the nuclear motion does not occur on the ground state electronic surface but it can, nonetheless, provide useful information.) In order to alleviate these difficulties the isokinetic methods of Paper I are applied to derive isokinetic CP equations of motion. The efficacy of the new isokinetic CPMD method is demonstrated on model and realistic systems. The latter include, metallic systems, liquid aluminum, a small silicon sample, the 2×1 reconstruction of the silicon 100 surface, and the Diels–Alder addition of 1,3-butadiene to the reconstructed silicon 100 surface.
Temperature dependence of droplet nucleation in a Yukawa fluid
Authors: Li Jin-Song , Wilemski Gerald
Published: January 2003

We have studied the temperature dependence of gas-to-liquid nucleation in Yukawa fluids with gradient theory and density functional theory. Each of these nonclassical theories exhibits a weaker (i.e., better) temperature dependence than classical nucleation theory. At fixed temperature, the reversible work to form a critical nucleus found from gradient theory approaches the value given by density functional theory as the supersaturation increases. At high temperatures, the two theories remain quite close over a wide range of vapor densities. As the temperature is reduced, the difference between the two theories increases with decreasing vapor density. Compared to the classical theory we find that gradient theory can improve the predicted temperature dependence of the nucleation rate, although not always to the same degree as density functional theory. Finally, our results show that the scaling behavior of density functional theory proposed by McGraw and Laaksonen can be extended to higher temperatures if the incompressibility assumption is avoided when evaluating the classical reversible work.
Energy transfer and device performance in phosphorescent dye doped polymer light emitting diodes
Authors: Noh Yong-Young , Lee Chang-Lyoul , Kim Jang-Joo , Yase Kiyoshi
Published: January 2003

Singlet and triplet–triplet energy transfer in phosphorescent dye doped polymer light emitting devices were investigated. Poly(N-vinylcarbazol) and poly[9,9′-di-n-hexyl-2,7-fluorene-alt- 1,4-(2,5-di-n-hexyloxy)phenylene] (PFHP) were selected as the host polymer for the phosphorescent dopants fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3] and 2,3,7,8,12,13, 17,18-octaethyl-21H,23H-porphyrin platinum(II) (PtOEP) because of their high triplet energy levels and long phosphorescence lifetimes. In case of PVK film, efficient triplet energy transfers to both PtOEP and Ir(ppy)3 were observed. In contrast, the triplet energy transfer did not occur or was very weak from PFHP to both PtOEP and Ir(ppy)3 although usual requirements for triplet energy transfer were satisfied. Furthermore, the singlet–singlet energy transfer did not take place from PFHP to Ir(ppy)3 in doped films even though the Förster radius is more than 30 Å. However, the blended film of Ir(ppy)3 with PFHP and PMMA showed the green emission from Ir(ppy)3 via singlet energy transfer. In addition, the solution of PFHP and Ir(ppy)3 (8 wt. %) in p-xylene also showed green emission. The blocking of the energy transfers in the phosphorescent dye doped PFHP films is found to be originated from the formation of aggregates which is evident from the microscopic images taken by transmission electron microscope, atomic force microscope, and fluorescence microscope. The formation of aggregates prevents dopant molecules from being in close proximity with host molecules thereby inhibiting energy transfer processes. The phase separation deteriorates the device performance also. Therefore, the chemical compatibility of a dopant with a host polymer as well as conventional requirements for energy transfers must be significantly considered to fabricate efficient phosphorescent dye doped polymer light emitting devices.
An ab initio molecular dynamics study of the SN2 reaction F−+CH3Cl→CH3F+Cl−
Authors: Mugnai Martina , Cardini Gianni , Schettino Vincenzo
Published: January 2003

The F−+CH3Cl→CH3F+Cl− reaction has been investigated by ab initio molecular dynamics with the Car–Parrinello method. The Hamprecht, Cohen, Tozer, and Handy exchange-correlation functional produces a stable prereactive complex. Thermal effects at 300 K have been calculated in the Blue Moon ensemble. An appreciable increase in the energy barrier has been obtained at 300 K relative to the 0 K. The averaged potential energy surface at 300 K shows the presence of a stable hydrogen bonded complex. Noncollinear impact trajectories have been examined. The transition state lifetime has been estimated. The energy redistribution among the degrees of freedom following the impact shows that a large part of the energy is localized in the C–F stretch and also in the umbrella bending.
Shear viscosity of molten sodium chloride
Authors: Delhommelle Jerome , Petravic Janka
Published: January 2003

The shear viscosity of molten sodium chloride is determined under a wide range of strain rates using nonequilibrium molecular dynamics (NEMD) simulations in the canonical (N,V,T) ensemble. Questions have been recently raised on the use of kinetic temperature thermostats, based on the equipartition principle, in simulations of nonequilibrium fluids and using a configurational temperature thermostat has been suggested to be more realistic. To further ascertain the results obtained in this work, we study molten NaCl with both kinetic and configurational temperature thermostats. Since configurational thermostats have been so far restricted to simple fluids or alkanes, we first apply configurational expressions for the temperature to molten NaCl, test the values so obtained in equilibrium molecular dynamics simulation for various system sizes and state points and finally use them to thermostat molten NaCl under shear. NEMD results obtained for both thermostats show that except for the so-called normal stress coefficients, molten salt under shear exhibits mostly the same features as a simple fluid under shear, i.e., features in agreement with the mode-coupling theory. The choice of the thermostatting method is found to have little influence on the results for the range of shear rates investigated.