β^-衰变的能量和强度平衡计算

论述了β-衰变的能量和强度平衡的计算公式,并以95Nb的β-衰变为例说明其实际应用。

Microstructure of cast γ-TiAl based alloy solidified from β phase region

The microstructures and phase transformation of Ti-43Al-4Nb alloy in as-cast and heat-treated states were investigated by using optical microscopy, scanning and transmission electron microscopy as well as differential scanning calorimetry. The results show that a fine microstructure of the as-cast alloy can be obtained by solidifying through the β phase. γ grains can nucleate directly from the β phase. The coexistence of β phase and γ phase along primary α grain boundaries contributes to the decrease in the grain size of the as-cast alloy. The phase transformation sequence during solidification of the Ti-43Al-4Nb alloy is suggested as L→L＋β→β→α＋β→α＋βr→α＋γ＋βr→lamellae（α2＋γ）＋γ＋βr. The microstructure of the alloy after heat treatment at 1 250 ℃ for 16 h exhibits a certain coarsening compared with that of the as-cast state. The remnant β phase can be removed by the heat treatment process due to the diffusion of Nb and the non-equilibrium state of β phase.

EFFECTS OF MICRO STRESS FIELD ON MARTENSITE TRANSFORMATION CHARACTERISTICS IN Ni-Ti-Nb BASED SHAPE MEMORY ALLOYS

The transformation behavior of Ni Ti Nb based alloys was analysed.The absence of R phase transformation in these alloys is related to the stress field in the NiTi matrix.The thermal mismatch stress was calculated by the Eshelby method in Ni Ti Nb alloys.The results show that the mean matrix elastic stress field is isostatic tensile,there is no preferred stress in [111] B 2 direction.The mean matrix stress from the thermal misfit between NiTi matrix and β Nb particle is too small to induce dislocations.All the factors tend to inhibit R phase transformation.

Deformation banding in β working of two-phase TA15 titanium alloy

To study deformation banding inβworking of TA15titanium alloy,hot simulation compression experiments were carried out on a Gleeble3500thermal simulator,and the microstructure was investigated by optical microscopy(OM)and electron backscattered diffraction(EBSD).It is found that inβworking of TA15titanium alloy,deformation banding is still an important grain refinement mechanism up to temperature as high as0.7Tm(Tm is the melting temperature).Boundaries of deformation bands(DBBs)may be sharp or diffusive.Sharp DBBs retard discontinuous dynamic recrystallization(DDRX)by prohibiting nucleation,while the diffusive ones are sources of continuous dynamic recrystallization(CDRX).Deformation banding is more significant at high strain rate and large initial grain size.The average width of grain subdivisions is sensitive to strain rate but less affected by temperature and initial grain size.Multi-directional forging which produces crossing DDBs is potential to refine microstructure of small-size forgings.

Mechanical alloying and phase transformation in Fe-Si alloy

The Fe-Si mechanical alloying and its transformation are investigated to evaluate whether mechanical alloying is a useful process for producing Fe-Si alloy. The mechanical alloying process of Fe-Si powders is studied by SEM（ scanning electron microscopy）, EDS（energy dispersive spectrometer）and XRD（X-ray diffraction）. The results show that the ball milling process first makes tough Fe powder a lump structure and brittle Si powder a small particle, and then as the mill power increases, the tough powder of iron with a lamellar structure forms and the Si particles lies on or between the Fe lamellas. Finally, the Fe and Si powders are mechanically alloyed through atom diffusion. So the Fe and Si powders can be alloyed by 15 h ball milling at a speed of 400 r/min and with a ball-to-powder ratio of 40 ： 1. After heating at 1 243 K for 1 h, the milled powders transform to α-FeSi2, and after heating at 1 243 K for 1 h, then cooling to 1 073 K for 1 h, the milled powders transform to β-FeSi2. Therefore, the monophase α-FeSi2 or β-FeSi2 can be obtained by heat treatment of mechanically alloyed Fe-Si powders.

Research progress on microstructure evolution and hot processing maps of high strength β titanium alloys during hot deformation

High strength β titanium alloys are widely used in large load bearing components in the aerospace field. At present, large parts are generally formed by die forging. Different initial microstructures and deformation process parameters will significantly affect the flow behavior. To precisely control the microstructures, researchers have conducted many studies to analyze the microstructure evolution law and deformation mechanism during hot compression. This review focuses on the microstructure evolution of high strength β titanium alloys during hot deformation, including dynamic recrystallization and dynamic recovery in the single-phase region and the dynamic evolution of the α phase in the two-phase region. Furthermore, the optimal hot processing regions, instability regions,and the relationship between the efficiency of power dissipation and the deformation mechanism in the hot processing map are summarized. Finally, the problems and development direction of using hot processing maps to optimize process parameters are also emphasized.

α″phase-assisted nucleation to obtain ultrafineαprecipitates for designing high-strength near-βtitanium alloys

The diffusion-multiple method was used to determine the composition of Ti−6Al−4V−xMo−yZr alloy(0.45<x<12,0.5<y<14,wt.%),which can obtain an ultrafine α phase.Results show that Ti−6Al−4V−5Mo−7Zr alloy can obtain an ultrafineαphase by using the α″phase assisted nucleation.The bimodal microstructure obtained with the heat-treatment process can confer the alloy with a good balance between the strength and plasticity.The deformation mechanism is the dislocation slip and the{1101}twinning in the primary α phase.The strengthening mechanism is α/β interface strengthening.The interface of(0001)α/(110)β has a platform−step structure,whereas(1120)α/(111)βinterface is flat with no steps.

First—Order—Like Transition for Dispersive Optical Bistability

The first-order-like phase transition (FOLT) in the dispersive optical bistability is investigated when the fluctuation in the incident light field is considered as colored noise. A unified colored-noise approximation is applied to obtain the steady state distribution (SSD) when either the intensity or phase fluctuations of the incident field are included in the system. For intensity fluctuations only, the curve of SSD is changed from single extreme to two extremes, and then to three extremes. The colored nature of the noise can reduce the fluctuation in the system. However, for phase fluctuations only, the FOLT is mainly induced by the colored nature of the noise. The curve of SSD is changed from single extreme to three extremes directly. There is no FOLT existing for white noise.

Magnetic Field Effect on β^＋ Decay in the Crusts of Accreting Neutron Stars

Based on shell model of nuclei, the influence of a high magnetic field on β^＋ decay in the crusts of accreting neutron stars is analyzed. The magnetic field effect on 54 Mn is discussed. The results show that a weak magnetic field makes little effect on β^＋ decay but a strong magnetic field （B 〉 10^11 G） improves β^＋ decay rates obviously. The conclusion derived will benefit to develop further research on nuclear astrophysics in the future.

Ab initio Study of the Potential Energy Surface and Product Branching Ratios for Reaction of O（^1D） with C2H5CI

The potential energy surface of O（^1D）＋C2H5Cl reaction was studied using QCISD（T）/6- 311＋＋G（d,p）//MP2/6-31G（d,p） method. The calculations reveal an insertion-elimination mechanism. The insertion reaction of O（^1D） and C2H5Cl produces two energy-rich intermediates, IM1 and IM2, which subsequently decompose into various products. The calculations of the branching ratios of various products formed through the two intermediates were carried out using RRKM （Rice-Ramsperger-Kassel-Marcus） theory at the collision energies of 0, 20.9, 41.8, 62.7, 83.6, 104.5, and 125.4 kJ/mol. HCl is the main decomposition product for IM1; CH2OH is the main decomposition product for IM2. Since IM1 is more stable than IM2, HCl is probably the main product of the O（^1D）＋C2H5Cl reaction.

A PHOTOEMISSIVE MONOENERGETIC ELECTRON SOURCE FOR CALIBRATING THE BETA－MAGNETIC SPECTROMETER

A new kind of electron source, the photoemissive monoenergetic electron source has been invented for calibrating the beta--magnetic spectrometer. It produceselectrons in the form of simulating a radioactive monoenergetic electron source andcan be made in any shape and size according tO the demands of experimentS. In thispaper, the principles and basic constructions of the photoemissive monoenergeticelectron source are described, the resultS of calibrating our 2’l’x bead--magneticspectrometer with a single strip arc shaped photoemissive monoenergetic electronsource are listed, a new way for determining resolution function of experimentslsystem in the research of neutrino rest mass has been posed and one of its actualapplications is also given.

Characterization of hot deformation and microstructure evolution of a new metastableβtitanium alloy

The hot deformation characteristics of as-forged Ti−3.5Al−5Mo−6V−3Cr−2Sn−0.5Fe−0.1B−0.1C alloy within a temperature range from 750 to 910℃and a strain rate range from 0.001 to 1 s^(-1) were investigated by hot compression tests.The stress−strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate.The microstructure is sensitive to deformation parameters.The dynamic recrystallization(DRX)grains appear while the temperature reaches 790℃at a constant strain rate of 0.001 s^(-1) and strain rate is not higher than 0.1 s^(-1) at a constant temperature of 910℃.The work-hardening rateθis calculated and it is found that DRX prefers to happen at high temperature and low strain rate.The constitutive equation and processing map were obtained.The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map,which indicates excellent hot workability.At the strain rate of 0.1 s^(-1),the stress−strain curves show an abnormal shape where there are two stress peaks simultaneously.This can be attributed to the alternation of hardening effect,which results from the continuous dynamic recrystallization(CDRX)and the rotation of DRX grains,and dynamic softening mechanism.

Mutation of DNA polymerase p in esophageal carcinoma of different regions

AIM： To observe the variation of DNA polymerase β （polβ） in esophageal carcinoma. METHODS： Thirty specimens containing adjacent normal epithelial tissues were collected from patients in Linzhou region （a high risk area for esophageal squamous carcinoma） and 25 specimens were from a non-high risk area. Total RNA was extracted from the samples and reverse transcription polymerase chain reaction （RT-PCR） was performed. PCR products were cloned and sequenced to investigate the po1β gene with DNASIS and OMIGA. Statistical significance was evaluated using the X^2 test. RESULTS： High-inddence area group： Polβ gene variation was detected in 13 of 30 esophageal carcinoma tissue specimens, and only one variation was found in 30 corresponding adjacent normal tissue specimens. Non high-incidence area group： po1β gene variation was detected in 5 of 25 esophageal carcinoma tissue specimens, and no variation was found in 25 corresponding adjacent normal tissue specimens. The incidence of po1β gene variation observed in the high-incidence area group was significantly higher than in the non-high incidence area group. Two mutation hot spots （454-466 and 648-670 nt） and a 58 bp deletion （177-234 nt） were found. CONCLUSION： Variations of polβ perform different functions between the high-incidence areas and the other areas, and may play a more important role in the high-incidence areas.

Effect of Acid Treatment on Interfacial and Foam Properties of Soy Proteins

The goal of the present work was to study the effects of acid treatment on the foaming properties of a soybean protein isolate （SPI） and its fractions, glycinin （11S） and β-conglycinin （7S）. The structural characteristics, interfacial properties, foaming capacity and stability of the treated proteins were studied. Results from surface hydrophobicity and differential scanning calorimetry （DSC） showed that the acid treatment caused the complete denaturation of 11S and a partial denaturation of 7S. This protein unfolding affected their interracial properties, which led to an improvement in the foaming properties of both protein fractions and isolate. Treated 7S showed the best behavior in the rearrangement process, probably due to its smaller size and its modified structural characteristics. All treated proteins showed stronger interracial films. The foams of treated proteins were destabilized mostly due to gravitational drainage rather than Ostwald ripening.

Empirical formula for β^--decay half-lives of r-process nuclei

Experimental data ofβ--decay half-lives of nuclei with atomic number between 20 and 190 are investigated.A systematic formula has been proposed to calculateβ^--decay half-lives of neutron-rich nuclei,with a particular consideration on shell and pair effects,the decay energy Q as well as the nucleon numbers(Z,N).Although the formula has relatively few parameters,it reproduces the experimentalβ^--decay half-lives of neutron-rich nuclei very well.The predicted half-lives for the r-process relevant nuclei obtained with the current formula serve as reliable input in the r-process model calculations.

PandaX: a liquid xenon dark matter experiment at CJPL

PandaX is a large liquid-xenon detector experiment usable for direct dark-matter detection and 136Xe double-beta decay search.The central vessel was designed to accommodate a staged target volume increase from initially 120 kg(stage I)to 0.5 t(stage II)and eventually to a multi-ton scale.The experiment is located in the Jinping Deep-Underground Laboratory in Sichuan,China.The detector operates in dual-phase mode,allowing detection of both prompt scintillation,and ionization charge through proportional scintillation.In this paper a detailed description of the stage I detector design and performance as well as results established during the commissioning phase are presented.

Panda X-III： Searching for neutrinoless double beta decay with high pressure ^(136)Xe gas time projection chambers

Searching for the neutrinoless double beta decay(NLDBD)is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments.Panda X-III(particle and astrophysical xenon experiment III)will search for the NLDBD of136Xe at the China Jin Ping Underground Laboratory(CJPL).In the first phase of the experiment,a high pressure gas Time Projection Chamber(TPC)will contain 200 kg,90%136Xe enriched gas operated at10 bar.Fine pitch micro-pattern gas detector(Microbulk Micromegas)will be used at both ends of the TPC for the charge readout with a cathode in the middle.Charge signals can be used to reconstruct the electron tracks of the NLDBD events and provide good energy and spatial resolution.The detector will be immersed in a large water tank to ensure～5 m of water shielding in all directions.The second phase,a ton-scale experiment,will consist of five TPCs in the same water tank,with improved energy resolution and better control over backgrounds.

β-decay studies approaching the N=20 island of inversion with a new shell-model Hamiltonian

β-decay properties of N=18-22,Z=10-14 nuclei are analyzed with a new shell-model Hamiltonian using the Gogny densitydependent interaction.The Gogny force which has been widely and successfully used in mean-field theory can provide reasonable two-body matrix elements for cross-shell calculations.The log f t values andβ-decay level schemes are systematically studied using the D1S-Gogny interaction and compared with the SDPF-M results and experimental data.It is shown that the new Hamiltonian provides reliable results forβ-decay along with subtle level schemes for this region.Shell-model calculations with Gogny interaction can lead to a successful description of nuclei in and around the N=20 island of inversion and supplements experiment where sufficient data are not available.

The ft values of the superallowed Fermi beta decays

In this work, the ft values of the 0+ →0+ superallowed Fermi beta decays have been investigated. In the calculations, the shell model has been modified by Pyatov's restoration method because of the isospin breaking and the transition matrix elements have been found by means of the quasi-particle random phase approximation (QRPA).

Regulatory T cells and asthma

Asthma is a chronic disease of airway inflammation due to excessive T helper cell type 2 （Th2） response. Present treatment based on inhalation of synthetic glucocorticoids can only control Th2-driven chronic eosinophilic inflammation, but cannot change the immune tolerance of the body to external allergens. Regulatory T cells （Tregs） are the main negative regulatory cells of the immune response. Tregs play a great role in regulating allergic, auto- immune, graft-versus-host responses, and other immune responses. In this review, we will discuss the classification and biological characteristics, the established immunomodulatory mechanisms, and the characteristics of induced differentiation of Tregs. We will also discuss the progress of TregS in the field of asthma. We believe that further studies on the regulatory mechanisms of Tregs will provide better treatments and control strategies for asthma.