The Effect of Radiogenic Heating on the Amino Acid Content of an Early Cometary Body

This study compares the rates for the formation and destruction of amino acids in the liquid cometary core subjected to radiogenic heating by the β+ decay of the cosmogenic nuclide 26Al. The evolution of the temperature and mass of the comet were computed along with the dynamics of relatively complex organic species such as amino acids. Given the experimentally determined rate coefficient for the radiolysis of amino acids in water solution, the destruction of amino acids is virtually completed after an absorbed radiation dose of ~1 kGy. The calculations suggest that the liquid water core in comets with an initial radionuclide abundance that is sufficient to crystallize and melt the original amorphous ice is subjected to a dose of 100 - 1500 kGy. Any amino acid concentration formed in water either by radiolysis of simpler compounds or by thermal processes such as the synthesis of Strecker could not survive the irradiation delivered by the decay of 26Al.

LOCAL SALINE APPROXIMATION METHODS FOR SINGULAR PRODUCT INTEGRATION

The purpose of this paper is to propose and study local spline approximation methods for singular product integration,for which;i)the precision degree is the highest possible using splint approximation; ii) the nodes fan be assumed equal to arbitrary points,where the integrand function f is known; iii) the number of the requested evaluations of f at the nodes is low,iv) a satisfactory convergence theory can be proved.

Percutaneous coronary intervention in nonagenarians: pros and cons

Percutaneous coronary intervention is a mainstay in the management of symptomatic or high-risk coronary artery disease. The bulk of clinical evidence and experience underlying this fact relies, however, on relatively young patients. Indeed, few data of very limited quality are available which adequately define the risk-benefit and cost-benefit profile of coronary angioplasty and stenting in very old subjects, such as those of 90 years of age or older (i.e., nonagenarians). The aim of this review is to provide a concise, yet practical, synthesis of the available evidence on percutaneous coronary revascularization in the very elderly. The main arguments elaborated upon are to what extent we can extrapolate findings from studies including younger patients to nonagenarians, whether we should provide higher priority to prognosis or quality of life in such patients, and whether we can afford to allocate vast resources to care for such subjects in an era of financial constraints. Our review of 18 studies and 1082 patients suggest that percutaneous coronary intervention is feasible and associated with acceptable short- and long-term results in this population, which is nonetheless fraught with a high mortality risk irrespective of the revascularization procedure. Accordingly, the pros and cons of percutaneous coronary intervention should be carefully weighed when considering this treatment in nonagenarians.

An extended assessment of bowel habits in a general population

AIM:Bowel habits are difficult to study, and most data on defecatory behaviour in the general population have been obtained on the basis of recalled interview. The objective assessment of this physiological function and its pathological aspects continues to pose a difficult challenge. The aim of this prospective study was to objectively assess the bowel habits and related aspects in a large sample drawn from thegeneral population.METHODS: Over a two-month period 488 subjects were prospectively recruited from the general population and asked to compile a daily diary on their bowel habits and associated signs and symptoms (the latter according to Rome Ⅱ criteria). A total of 298 (61%) participants returned a correctly compiled record, so that data for more than 8000 patient-days were available for statistical analysis.RESULTS:The average defecatory frequency was once per day (range of 0.25-3.25) and was similar between males and females.However, higher frequencies of straining at stool (P=0.001), a feeling of incomplete emptying and/or difficult evacuation (P=0.0001), and manual manoeuvres to facilitate defecation (P=0.046) were reported by females as compared to males.CONCLUSION:This study represents one of the first attempts to objectively and prospectively assess bowel habits in a sample of the general population over a relatively long period of time. The variables we analyzed are coherent with the criteria commonly used for the clinical assessment of functional constipation, and can provide a useful adjunt for a better evaluation of constipated patients.

A potential energy profile of the catalytic cycle of pyruvate decarboxylase

A computational study on the mechanism for the decarboxylation of pyruvic acid to acetaldehyde catalyzed by pyruvate decarboxylase at the B3LYP/6-31G (d, p) level of theory is presented. The model employed is self-contained and it does not resort to external groups to provide protons to the various structures in the mechanism. The potential energy surface points at the intramolecular proton transfer from the amino group of the pyrimidine ring in the enamine intermediate to the enol exocyclic carbon as the rate-determining step (with a barrier of 20.55 kcal·mol–1). This value is in reasonable agreement with an estimated barrier of 24.76 kcal·mol–1, derived from the experimental rate constant (4.0 10–5 s–1) for the decarboxylation of α-lactylthiamin.

The role of catalysis on the formation of an active proto-enzyme in the prebiotic aqueous environment

A model detailing the conditions for the formation of active enzymes from amino acid monomers in the pre-biotic aqueous environment is proposed, making use of only a minimal number of parameters: the intensity of the amino acid source and the experimental rate coefficient for polypeptide hydrolysis. In a closed system with fixed total amino acid concentration, the formation of polypeptides of significant length is precluded by hydrolysis. In the presence of an amino acid source, the behavior of the steady state solutions is dependent on the efficiency of the catalytic activity in the environment. In absence of catalysis the formation of long amino acid chains shows a remarkable similarity to the equilibrium problem, i.e. it is equally unlikely that an active protein forms. In the presence of catalysis the concentration of polypeptides of significant length increases dramatically to about the same order of magnitude as the steady state concentration of the monomers. Besides the important notion of the proto-enzyme concentration, the model offers a link between the given environmental conditions (flux of monomers, rates of the peptide bond formation and hydrolysis, size of the amino acid set) and properties of the polypeptide relevant to its catalytic properties, such as its length and conserved number of residues.

Crystallization Kinetics and Magnetic Properties of Fe₄₀Ni₄₀B₂₀Bulk Metallic Glass

Fe-based bulk metallic glasses (BMGs) have been extensively studied due to their potential technological applications and their interesting physical properties such as a low modulus of elasticity, high yielding stress and good magnetic properties. In the present work, the bulk metallic glass (BMG) formation of Fe40Ni40B20 (numbers indicate at %) with a ribbon form was fabricated by the single roller melt-spinning method. Rapid solidification leads to a fully amorphous structure for all compositions. The thermal properties associated with crystallization temperature of the glassy samples were measured using differential scanning calorimetry (DSC) at a heating rate of 10℃/mn. The microstructure and constituent phase of the alloy composite have been analyzed by using X-ray diffractometry (XRD). The effect of high temperature on the isothermal crystallization of Fe40Ni40B20 ribbon was investigated by HTX-ray diffraction. In addition, these ribbon glasses also exhibit good soft magnetic properties with M-H curvature measured under the magnetic fields between –1 kOe and 1 kOe.

慢性炎症性脱髓鞘性多发性神经病患者膈神经的亚临床电生理学改变

Alterations of the phrenic nerve (PN) and pulmonary function tests (PFTs) have been described in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). This study was aimed at assessing the relationship between PN and respiratory function in CIDP patients without clinical signs of respiratory failure. Bilateral PN and right median nerve conduction studies were carried out along with blood gas analysis and PFTs: maximal inspiratory pressure; maximal expiratory pressure; forced vital capacity. The amplitude of the compound muscle action potential of the PN was seen to be altered in 19/24 (79%) patients and latency in 22 (92%). Eighteen patients (75%) showed at least one abnormal PFTs or CO2 partial pressure value. Electrophysiological alterations of the PN were observed in a high percentage of the CIDP patients studied. No statistically significant correlation was observed between PN and PFTs alterations.

A model to explain the angular distribution of J/Ψ and Ψ(2S) decay into ■ and ■

BESⅢ data show a particular angular distribution for the decay of J/Ψ and Ψ(2 S) mesons into ■ and Σ~0Σ~0 hyperons: the angular distribution of the decay Ψ(2 S) →Σ~0Σ~0 exhibits an opposite trend with respect to the other three channels: J/Ψ→■, J/Ψ→Σ~0Σ~0 and Ψ(2 S) →■. We define a model to explain the origin of this phenomenon.

Exploitation of symmetry in periodic Self-Consistent-Field ab initio calculations: application to large three-dimensional compounds

Symmetry can dramatically reduce the computational cost(running time and memory allocation) of Self-Consistent-Field ab initio calculations for crystalline systems. Crucial for running time is use of symmetry in the evaluation of one- and two-electron integrals, diagonalization of the Fock matrix at selected points in reciprocal space, reconstruction of the density matrix. As regards memory allocation, full square matrices(overlap, Fock and density) in the Atomic Orbital(AO) basis are avoided and a direct transformation from the packed AO to the SACO(Symmetry Adapted Crystalline Orbital) basis is performed, so that the largest matrix to be handled has the size of the largest sub-block in the latter basis. We here illustrate the effectiveness of this scheme, following recent advancements in the CRYSTAL code, concerning memory allocation and direct basis set transformation. Quantitative examples are given for large unit cell systems, such as zeolites(all-silica faujasite and silicalite MFI) and garnets(pyrope). It is shown that the full SCF of 3D systems containing up to 576 atoms and 11136 Atomic Orbitals in the cell can be run with a hybrid functional on a single core PC with 500 MB RAM in about 8 h.

Vegetation and Topographic Control on Spatial Variability of Soil Organic Carbon

Soil organic carbon (SOC) is one of the most important parameters affecting the hydraulic characteristics of natural soils. Despite being rather easy to measure, SOC is known to be highly variable in space. In this study, vegetation, climate, and morphology factors were used to reproduce the spatial distribution of SOC in the mineral horizons of forest and grassland areas in north-western Italy and the feasibility of the approach was evaluated. When the overall sample (114 samples) was analyzed, average annual rainfall and elevation were significant descriptors of the SOC variability. However, a large part of the variability remains unexplained. Two stratification criteria were then adopted, based on vegetation and topographic properties. We obtained an improvement of the quality of the estimates, particularly for grasslands and forests in the absence of local curvatures. These results indicate that the spatial variability of soil organic matter is scarcely reproducible at the regional scale, unless an a-priori reduction of the heterogeneity is applied. A discussion on the feasibility of applying stratification criteria to deal with heterogeneous samples closes the paper.

Sensor Deployment and Relocation:A Unified Scheme

Sensor networks are envisioned to revolutionize our daily life by ubiquitously monitoring our environment and/or adjusting it to suit our needs. Recent progress in robotics and low-power embedded systems has made it possible to add mobility to small, light, low-cost sensors to be used in teams or swarms. Augmenting static sensor networks with mobile nodes addresses many design challenges that exist in traditional static sensor networks. This paper addresses the problem of topology control in mobile wireless networks. Limitations in communication, computation and energy capabilities push towards the adoption of distributed, energy-efficient solutions to perform self-deployment and relocation of the nodes. We develop a unified, distributed algorithm that has the following features. During deployment, our algorithm yields a regular tessellation of the geographical area with a given node density, called monitoring configuration. Upon the occurrence of a physical phenomenon, network nodes relocate themselves so as to properly sample and control the event, while maintaining the network connectivity. Then, as soon as the event ends, all nodes return to the monitoring configuration. To achieve these goals, we use a virtual force-based strategy which proves to be very effective even when compared to an optimal centralized solution. We assess the performance of our approach in the presence of events with different shapes, and we investigate the transient behavior of our algorithm. This allows us to evaluate the effectiveness and the response time of the proposed solution under various environmental conditions.

Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.

The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called ＂knee＂ by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber （RPC） array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range （100-700 TeV）. The observed energy spectrum is compatible with a single power law with index γ=-2.63±0.06.

Latest results from GRAAL collaboration

The GRAAL experimental set-up consists of a polarized and tagged photon beam that covers an energy range from a minimum of 600 MeV up to a maximum of 1500 MeV, of a liquid Hydrogen or Deuterium target and of the 4π Lagrange detector optimized for photon detection. It allows the study of pseudo-scalar and vector meson photoproduCtion on the nucleon in the energy range corresponding to the second and the third resonance regions. In the following, the ∑ beam asymmetries in η and π0 photoproduction on quasi-free nucleon are shown. Also single and double polarization observables in K＋A photoproduction on free proton are shown; they are important to confirm the role of new or poorly known resonances in the 1900 MeV mass region.