Orbits in the H(2)O molecule

We study the forms of the orbits in a symmetric configuration of a realistic model of the H(2)O molecule with particular emphasis on the periodic orbits. We use an appropriate Poincare surface of section (PSS) and study the distribution of the orbits on this PSS for various energies. We find both ordered and chaotic orbits. The proportion of ordered orbits is almost 100% for small energies, but decreases abruptly beyond a critical energy. When the energy exceeds the escape energy there are still nonescaping orbits around stable periodic orbits. We study in detail the forms of the various periodic orbits, and their connections, by providing appropriate stability and bifurcation diagrams. (c) 2001 American Institute of Physics.     

Reaction of the oxygen molecule at the Si(100)-SiO2 interface during silicon oxidation

Using constrained ab initio molecular dynamics, we investigate the reaction of the O2 molecule at the Si(100)-SiO2 interface during Si oxidation. The reaction proceeds sequentially through the incorporation of the O2 molecule in a Si-Si bond and the dissociation of the resulting network O2 species. The oxidation reaction occurs nearly spontaneously and is exothermic, irrespective of the O2 spin state or of the amount of excess negative charge available at the interface. The reaction evolves through the generation of network coordination defects associated with charge transfers. Our investigation suggests that the Si oxidation process is fully governed by diffusion.     

Frequency- and level-dependent changes in auditory brainstem responses (ABRS) in developing mice

The development of the auditory brainstem response was studied to quantitatively assess its dependence on stimulus frequency and level. Responses were not observed to stimuli > or =16 kHz on P12, however, the full range of responsive frequencies included in the study was observed by P14. Response thresholds were high on P12, exceeding 100 dB SPL for all stimuli tested. The rate of threshold development increased progressively for stimulus frequencies between -2 and 10 kHz, with the most rapid changes occurring at frequencies >10 kHz. Adultlike thresholds were observed by P18. Response latencies and interpeak intervals matured rapidly over the course of the second and third postnatal weeks and did not achieve adultlike characteristics until after P18. Latencies of higher-order peaks were progressively and sequentially delayed relative to wave I. Wave I amplitudes developed nonmonotonically, growing during the first 24 days and stabilizing at adult values by approximately P36. Slopes of wave I amplitude-and latency-level curves were significantly steeper than those of adults during the neonatal period and the outcome of input-output analyses, as well as frequency-specific maturational profiles, support developmental models in which function initially matures in the mid-frequency range and proceeds, simultaneously, in both apical and basal directions.     

Both systemic and local application of Granulocyte-colony stimulating factor (G-CSF) is neuroprotective after retinal ganglion cell axotomy

Background  

The hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) plays a crucial role in controlling the number of neutrophil progenitor cells. Its function is mediated via the G-CSF receptor, which was recently found to be expressed also in the central nervous system. In addition, G-CSF provided neuroprotection in models of neuronal cell death. Here we used the retinal ganglion cell (RGC) axotomy model to compare effects of local and systemic application of neuroprotective molecules.     

A time-resolved total internal reflection aqueous fluorescence (TIRAF) microscope for the investigation of cell adhesion dynamics

To investigate dynamic processes of cell adhesion on smooth and structured surfaces we developed a time-resolved TIRAF microscope with high spatial and temporal resolution. A lateral image resolution, close to the resolution limit of 223 nm, is reached using a variable microchannel with maximum height of 210 μm for cell cultivation in combination with a ×60 oil immersion objective of numerical aperture 1.4. Using Rhodamine Green as aqueous volume marker, no significant cell membrane damage occurs within 100 min under continuous irradiation in our experimental conditions. In time-discrete experiments with L929 cells over a period of 11 h we observed interactions of adhesion areas with the surface to which the cell adhered. Short-term measurements of a defined area of a single cell containing only a few adhesion contacts showed interactions between single adhesion clusters and also putative formation of new clusters. Stationary TIRAF experiments with cells growing on structured surfaces or between microelectrodes are possible without producing additional reflections. We conclude from our first results that time-resolved TIRAF microscopy is a powerful technique for studying the mechanism of cell motion, especially under a variety of artificial conditions used to influence cell migration. Received: 21 December 1998 / Accepted: 6 January 1999 / Published online: 7 April 1999     

Glycosaminoglycans and glycoconjugates in the adult anuran integument (Lithobates catesbeianus)

Glycosaminoglycans (GAGs) from the integument of Lithobates catesbeianus were biochemically characterized and histochemically localized. Moreover, carbohydrate distribution was investigated using conventional and lectin histochemistry at light microscopy. Hyaluronan (HA), dermatan sulfate (DS) and a heparanoid were found in the integument. Sulfated and carboxylated GAGs were visualized in the Eberth-Katschenko (EK) layer, in the mucous glands, in the hypodermis as well as in the mast cells. Furthermore, glucose and galactose were identified in the integument through thin layer chromatography (TLC) assays. N-Acetyl-β-glucosamine residues were identified in the mucous glandular cells, between the corneum and spinosum strata, in the subepidermal region, and in the EK layer. N-Acetyl-galactosamine residues were evident in the EK layer, corresponding to a residue of the dermatan sulfate chain, which may be related to the collagenous fiber arrangement. These glycoconjugates occurred as secretory glandular products and as dermal structural elements. Moreover, HA and DS are the predominant GAGs in the L. catesbeianus integument. Considering the importance of glycoconjugates, they play a significant role to the integrity of the skin, providing mechanical support for integument cells. In addition, they are important to the water regulation mechanisms, since L. catesbeianus is preferably aquatic.     

Band spectrum of the molecule germanium monoxide (GeO) in the visible region

Thermal emission spectrum of the molecule GeO has been recorded in the visible region λλ 5100-4600 for the first time, using a high temperature vacuum graphite furnace. Bands observed are red-degraded and constitute a new system which appears to be an analog of the B systems observed in the case of PbO and SnO.     

Intermolecular double quantum coherences (iDQc) and diffusion-weighted imaging (DWI) imaging of the human brain at 1.5 T

To study the sensitivity of intermolecular double quantum coherences (iDQc) imaging contrast to brain microstructure and brain anisotropy, we investigated the iDQC contrast between differently structured areas of the brain according to the strength and the direction of the applied correlation gradient. Thus diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) maps have been obtained. This procedure, which consists of analyzing both iDQc and DWI images at different gradient strength and gradient direction, could be a promising tool for clinical brain investigations performed with higher than 1.5 T magnetic fields.     

Measuring hearing in the harbor seal (Phoca vitulina): comparison of behavioral and auditory brainstem response techniques

Auditory brainstem response (ABR) and standard behavioral methods were compared by measuring in-air audiograms for an adult female harbor seal (Phoca vitulina). Behavioral audiograms were obtained using two techniques: the method of constant stimuli and the staircase method. Sensitivity was tested from 0.250 to 30 kHz. The seal showed good sensitivity from 6 to 12 kHz [best sensitivity 8.1 dB (re 20 microPa2 x s) RMS at 8 kHz]. The staircase method yielded thresholds that were lower by 10 dB on average than the method of constant stimuli. ABRs were recorded at 2, 4, 8, 16, and 22 kHz and showed a similar best range (8-16 kHz). ABR thresholds averaged 5.7 dB higher than behavioral thresholds at 2, 4, and 8 kHz. ABRs were at least 7 dB lower at 16 kHz, and approximately 3 dB higher at 22 kHz. The better sensitivity of ABRs at higher frequencies could have reflected differences in the seal's behavior during ABR testing and/or bandwidth characteristics of test stimuli. These results agree with comparisons of ABR and behavioral methods performed in other recent studies and indicate that ABR methods represent a good alternative for estimating hearing range and sensitivity in pinnipeds, particularly when time is a critical factor and animals are untrained.     

The ortho-(p Μp) molecule and muon absorption in liquid hydrogen

Muon absorption rates in atomic and molecular states of hydrogen are calculated taking account of all known effects other than electromagnetic radiative corrections, to an estimated accuracy of one percent. The measured molecular absorption rate is found to agree very well with the rate to be expected on the basis of muon-electron equivalence.     

Dynamic stability and thermodynamic characterization in an enzymatic reaction at the single molecule level

In this work we study, at the single molecular level, the thermodynamic and dynamic characteristics of an enzymatic reaction comprising a rate limiting step. We investigate how the stability of the enzyme-state stationary probability distribution, the reaction velocity, and its efficiency of energy conversion depend on the system parameters. We employ in this study a recently introduced formalism for performing a multiscale thermodynamic analysis in continuous-time discrete-state stochastic systems.     

What can we learn from the decay of NX(1625) in the molecule picture?

Considering two assumptions on the molecular state, i.e. the S-wave Λ̄–K^- and S-wave Σ̄⁰–K^- molecular states, we study the possible decays of N̄_X(1625) that include N̄_X(1625)→K^-Λ̄,π⁰p̄,ηp̄,π^-n̄. Our results indicate that (1) if N̄_X(1625) is the Λ̄–K^- molecular state, K^-Λ̄ is the main decay mode of N̄_X(1625), and the branching ratios of the rest decay modes are tiny; (2) if N̄_X(1625) is the Σ̄⁰–K^- molecular state, the branching ratio of N̄_X(1625)→K^-Λ̄ is one or two orders smaller than that of N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄. Thus the search for N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄ will be helpful to shed light on the nature of N̄_X(1625). PACS 13.30.Eg, 13.75.Jz     

Theoretical analysis of the coupling between Feshbach states and hyperfine excited states in the creation of ~(23)Na~(40)K molecule

We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of ~(23)Na~(40)K ground-state molecules.We use coupled-channel method to calculate the wave function of the Feshbach molecules,and give the short-range wave function of triplet component.The energies of the hyperfine excited states and the coupling strength between the Feshbach states and the hyperfine excited states are calculated.Our results can be used to prepare a specific hyperfine level of the rovibrational ground state to study the ultracold collisions involving molecules.     

Masked auditory thresholds in three species of birds, as measured by the auditory brainstem response (L)

Auditory brainstem responses (ABRs) were recorded in adult budgerigars, canaries, and zebra finches in quiet and in three levels of white noise for tone stimuli between 1 and 4 kHz. Similar to behavioral results, masked ABR thresholds increased linearly with increasing noise levels. When the three species are considered together, ABR-derived CRs were higher than behavioral CRs by 18-23 dB between 2 and 4 kHz and by about 30 dB at 1 kHz. This study clarifies the utility of using ABRs for estimating masked auditory thresholds in natural environmental noises in species that cannot be tested behaviorally.     

Poly(ADP-ribose) polymerase-1 gene in human tumor cell lines: Its expression and structural alteration

Poly(ADP-ribose) polymerase-1 (Parp-1) is involved in DNA repair and cell-death induction after DNA damage. Parp-1^−/− mice show higher susceptibility to the carcinogenic effects of nitrosamine and azoxymethane. To elucidate the role of alterations of the PARP-1 gene in human carcinogenesis, we examined the expression level of PARP-1 gene in various human tumor cell lines. The presence of gross rearrangement of PARP-1 gene in these cell lines was also examined by Southern blot hybridization analysis. The expression levels of PARP-1 gene in several cell lines, including T-cell leukemia cell lines (Molt-4 and CCRF-CEM), colon cancer cell line (WiDr), and gastric cancer cell lines (KATOIII, OKAJIMA, and MKN45) was substantially lower than in other cancer cell lines. Among the 85 analyzed cell lines, structural alteration of PARP-1 gene was detected in a gastric cancer cell line, MKN28. A low level of PARP-1 expression in human cancer could potentially influence cancer cell growth, differentiation and cancer development by affecting genomic instability, as well as the response of tumors to chemo- and radiotherapy.     

Novel peak assignments of in vivo (13)C MRS in human brain at 1.5 T

(13)C MRS studies at natural abundance and after intravenous 1-(13)C glucose infusion were performed on a 1.5-T clinical scanner in four subjects. Localization to the occipital cortex was achieved by a surface coil. In natural abundance spectra glucose C(3beta,5beta), myo-inositol, glutamate C(1,2,5), glutamine C(1,2,5), N-acetyl-aspartate C(1-4,C=O), creatine CH(2), CH(3), and C(C=N), taurine C(2,3), bicarbonate HCO(-)(3) were identified. After glucose infusion (13)C enrichment of glucose C(1alpha,1beta), glutamate C(1-4), glutamine C(1-4), aspartate C(2,3), N-acetyl-aspartate C(2,3), lactate C(3), alanine C(3), and HCO(-)(3) were observed. The observation of (13)C enrichment of resonances resonating at >150 ppm is an extension of previously published studies and will provide a more precise determination of metabolic rates and substrate decarboxylation in human brain.