We report the first measurement of the structure of 4He atoms adsorbed on bundles of single-walled carbon nanotubes. Neutron diffraction techniques and nanotube samples closed at the end were used. ...At low coverage, 4He forms a 1D, single line lattice along the grooves between two nanotubes on the surface of the nanotube bundles. As coverage is increased, additional lines of 1D lattices form along the grooves. This is followed by an incommensurate, 2D monolayer covering the whole nanotube bundle surface. The lattice constants of these 1D and 2D systems are largely independent of filling once a single 1D line is formed. No occupation of the interstitial channels between nanotubes is observed in the present sample.
1. We investigated the ability of humans to tactually discriminate the softness of objects, using novel elastic objects with deformable and rigid surfaces. For objects with deformable surfaces, we ...cast transparent rubber specimens with variable compliances. For objects with rigid surfaces ("spring cells") we fabricated telescoping hollow cylinders with the inner cylinder supported by several springs. To measure the human discriminability and to isolate the associated information-processing mechanisms, we performed psychophysical experiments under three conditions: 1) active touch with the normal finger, where both tactile and kinesthetic information was available to the subject: 2) active touch with local cutaneous anesthesia, so that only kinesthetic information was available; and 3) passive touch, where a computer-controlled mechanical stimulator brought down the compliant specimens onto the passive fingerpad of the subject, who therefore had only tactile information. 2. We first characterized the mechanical behavior of the human fingerpad and the test objects by determining the relationship between the depth and force of indentation during constant-velocity indentations by a rigid probe. The fingerpad exhibited a pronounced nonlinear behavior in the indentation depth versus force trace such that compliance, as indicated by the local slope of the trace, decreased with increases in indentation depth. The traces for all the rubber specimens were approximately linear, indicating a constant but distinct value of compliance for each specimen. The fingerpad was more compliant than each of the rubber specimens. 3. All the human subjects showed excellent softness discriminability in ranking the rubber specimens by active touch, and the subjective perception of softness correlated one-to-one with the objectively measured compliance. The ability of subjects to discriminate the compliance of spring cells was consistently poorer compared with that of the rubber specimens. 4. For pairwise discrimination of a selected set of rubber specimens, kinesthetic information alone was insufficient. However, tactile information alone was sufficient, even when the velocities and forces of specimen application were randomized. In contrast, for discriminating pairs of spring cells, tactile information alone was insufficient, and both tactile and kinesthetic information were found to be necessary. 5. The differences in the sufficiency of tactile information for the discrimination of the two types of objects can be explained by the mechanics of contact of the fingerpad and its effect on tactile information. For objects with deformable surfaces, the spatial pressure distribution within the contact region depends on both the force applied and the specimen compliance.
Titanium alloys display low density, high mechanical strength and good corrosion resistance, being ideal structural materials for aerospace engineering. In this paper, the effects of nitrogen on the ...anelastic properties of the bcc alloy Ti-13V-11Cr-3Al were investigated. The results show an asymmetric thermally activated relaxation structure in the high-temperature region. This relaxation structure was decomposed, and relaxation processes due to stress-induced ordering of nitrogen atoms around the metallic matrix and substitutional solutes were identified.
ABSTRACT We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to γ-rays, during the 4.5 year period of ARGO-YBJ and Fermi common operation ...time, from 2008 August to 2013 February. These long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of Mrk 421. In particular, due to the ARGO-YBJ and Fermi data, the entire energy range from 100 MeV to 10 TeV is covered without any gap. In the observation period, Mrk 421 showed both low- and high-activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. The X-ray flux is clearly correlated with the TeV γ-ray flux, while the GeV γ-rays only show a partial correlation with the TeV γ-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and γ-ray fluxes. Seven large flares, including five X-ray flares and two GeV γ-ray flares with variable durations (3-58 days), and one X-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. During the outburst phase and the seven flaring episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV γ-ray flux increases up to 0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV γ-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the GeV flux variation. Finally, the one-zone synchrotron self-Compton model was adopted to describe the emission spectra. Two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. The underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties.
Dementia with Lewy bodies (DLB) is a neuropsychiatric disease associated with extrapyramidal features which differ from those of Parkinson's disease, including reduced effectiveness of L-dopa and ...severe sensitivity reactions to neuroleptic drugs. Distinguishing Alzheimer's disease from DLB is clinically relevant in terms of prognosis and appropriate treatment. Dopaminergic activities have been investigated at coronal levels along the rostrocaudal striatal axis from a post-mortem series of 25 DLB, 14 Parkinson's disease and 17 Alzheimer's disease patients and 20 elderly controls. 3HMazindol binding to the dopamine uptake site was significantly reduced in the caudal putamen in DLB compared with controls (57%), but not as extensively as in Parkinson's disease (75%), and was unchanged in Alzheimer's disease. Among three dopamine receptors measured (D1, D2 and D3), the most striking changes were apparent in relation to D2. In DLB, 3Hraclopride binding to D2 receptors was significantly reduced in the caudal putamen (17%) compared with controls, and was significantly lower than in Parkinson's disease at all levels. D2 binding was significantly elevated at all coronal levels in Parkinson's disease compared with controls, most extensively in the rostral putamen (71%). There was no change from the normal pattern of D2 binding in Alzheimer's disease. The only significant alteration in D1 binding (3HSCH23390) in the groups examined was an elevation (30%) in the caudal striatum in Parkinson's disease. There were no differences in D3 binding, measured using 3H7-OH-DPAT, in DLB compared with controls. A slight, significant decrease in D3 binding in the caudal striatum of Parkinson's disease (13%) patients and an increase in Alzheimer's disease (20%) in the dorsal striatum at the level of the nucleus accumbens were found. The concentration and distribution of dopamine were disrupted in both DLB and Parkinson's disease, although in the caudate nucleus the loss of dopamine in DLB was uniform whereas in Parkinson's disease the loss was greater caudally. In the caudal putamen, dopamine was reduced by 72% in DLB and by 90% in Parkinson's disease. The homovanillic acid : dopamine ratio, a metabolic index, indicated compensatory increased turnover in Parkinson's disease, which was absent in DLB despite the loss of substantia nigra neurons (49%), dopamine and uptake sites. These differences between DLB, Parkinson's disease and Alzheimer's disease may explain some characteristics of the extrapyramidal features of DLB and its limited response to L-dopa and severe neuroleptic sensitivity. The distinct changes in the rostrocaudal pattern of expression of dopaminergic parameters are relevant to the interpretation of the in vivo imaging and diagnosis of DLB.
In electric trains, a pantograph is mounted on the roof of the train to collect power through contact with an overhead catenary wire. The carbon-strip suspension of a pantograph, along which contact ...with the catenary occurs, is subjected to harmonic and stochastic contact-force excitations. In this paper, vertical dynamics of the carbon-strip suspension is studied with an aim of improving the reliability and safety of running trains. A single-degree-of-freedom model of the carbon-strip suspension with nonlinear stiffness is developed using parameter values of the DSA X pantograph. Through stochastic averaging, a Fokker–Planck–Kolmogorov equation governing the stationary response of the carbon-strip suspension is set up. Based on the transition probability density of the stationary response, it is found that random jumps and bifurcations in the carbon-strip motion can occur. The possibility of motion bifurcations and the frequency of random jumps warrant consideration in advanced design of carbon-strip suspensions.
•Flux to the target of Proto-MPEX is measured to be 5 ± 2.5 × 1023 m−2s-1 for helicon only plasmas.•Improved visible camera analysis of Balmer emission in front of plasma target.•Helicon plasma ...source alone does not create high recycling regime.
The ITER divertor will have to handle the boundary plasma power exhaust in the form of high heat and particle flux. The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a plasma source development device for the proposed Material Plasma Exposure eXperiment (MPEX), which is intended to create fusion reactor divertor-like plasma conditions for studying plasma material interactions. Here, ion fluxes to various targets within Proto-MPEX are found to be 5 ± 2.5 × 1023 m−2s-1 when using only a helicon plasma source. The fluxes along the flux tube are compared for both 30 cm in front of the target and a few cm in front of the target. The emission intensity fall-off distance in front of the target is studied via Balmer series from a visible camera looking at the target. This fall-off distance of ∼2–4 cm and the dissociation and ionization mean free path of D2 being over 0.5 m leads to a conclusion that Proto-MPEX is not in a high recycling regime with helicon only plasmas.
“U” curve association of blood pressure and mortality in hemodialysis patients.
Hypertension may play an important role in the pathogenesis of the excess cardiovascular and cerebrovascular (CV) ...morbidity observed in hemodialysis patients (HD). However, the optimal blood pressure (BP) range for HD patients has not been defined. We postulated that there is a “U” curve relationship between BP and CV mortality. To explore this hypothesis we studied 5,433 HD patients in Dialysis Clinic Inc., a large not-for-profit chain, over a five year period.
Cox regression, with fixed and time-varying covariates, was used to assess the effect of systolic blood pressure (SBP) and diastolic blood pressure (DBP), pre- and post-dialysis, on CV mortality, while adjusting for age, gender, ethnicity, primary cause of end-stage renal disease, Kt/V, serum albumin, and antihypertensive medications.
The overall impact of BP on CV mortality was modest. Pre-dialysis, neither systolic nor diastolic hypertension were associated with an increase in CV mortality. Post-dialysis, SBP ≥ 180mm Hg (RR = 1.96, P < 0.015) and DBP ≥ 90mm Hg (RR = 1.73, P < 0.05) were associated with increased CV mortality. Low SBP (SBP < 110mm Hg) was associated with increased CV mortality, pre- and post-dialysis.
The results suggest the presence of a “U” curve relationship between SBP post-dialysis and CV mortality in HD patients.
Spontaneous bioelectric activity (SBA) taking the form of extracellularly recorded spike trains (SBA) has been quantitatively analyzed in organotypic neonatal rat visual cortex explants at different ...ages in vitro, and the effects investigated of both short- and long-term pharmacological suppression of glutamatergic synaptic transmission. In the presence of APV, a selective NMDA receptor blocker, 1–2- (but not 3-)week-old cultures recovered their previous SBA levels in a matter of hours, although in imitation of the acute effect of the GABAergic inhibitor picrotoxin (PTX), bursts of action potentials were abnormally short and intense. Cultures treated either overnight or chronically for 1–3 weeks with APV, the AMPA/kainate receptor blocker DNQX, or a combination of the two were found to display very different abnormalities in their firing patterns. NMDA receptor blockade for 3 weeks produced the most severe deviations from control SBA, consisting of greatly prolonged and intensified burst firing with a strong tendency to be broken up into trains of shorter spike clusters. This pattern was most closely approximated by acute GABAergic disinhibition in cultures of the same age, but this latter treatment also differed in several respects from the chronic-APV effect. In 2-week-old explants, in contrast, it was the APV+DNQX treated group which showed the most exaggerated spike bursts. Functional maturation of neocortical networks, therefore, may specifically require NMDA receptor activation (not merely a high level of neuronal firing) which initially is driven by endogenous rather than afferent evoked bioelectric activity. Putative cellular mechanisms are discussed in the context of a thorough review of the extensive but scattered literature relating activity-dependent brain development to spontaneous neuronal firing patterns.
Glutamate synthase is a multicomponent iron-sulfur flavoprotein belonging to the class of N-terminal nucleophile amidotransferases. It catalyzes the conversion of L-glutamine and 2-oxoglutarate into ...two molecules of L-glutamate. In recent years the X-ray structures of the ferredoxin-dependent glutamate synthase and of the a subunit of the NADPH-dependent glutamate synthase have become available. Thanks to X-ray crystallography, it is now known that the ammonia reaction intermediate is transferred via an intramolecular tunnel from the amidotransferase domain to the synthase domain over a distance of about 32A. Although ammonia channeling is a recurrent theme for N-terminal nucleophile and triad-type amidotransferases, the molecular mechanisms of ammonia transfer and its control are different for each known amidotransferase. This review focuses on the intriguing mechanism of action and self-regulation of glutamate synthase with a special focus on the structural data.
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