Constraining the annihilation of dark matter via cosmic-ray positrons and electrons

We aim to constrain the properties of dark matter particles by several measurements of positrons and electrons from cosmic-rays. We assume that collisions of dark matter particles and dark matter anti-particles can produce positrons and electrons. The electron-positron propagation is explained by a diffusion-loss equation including loss rates, diffusion, as well as source function. We use data of cosmic-ray positrons and electrons detected by PAMELA, H.E.S.S., AMS-02 and Fermi-LAT. We compare the observational data with the electron and positron spectrum from five annihilation channels in our model to derive constraining factors regarding the cross-section of the annihilation of dark matter. The tightest constraint is provided by cosmic-ray positrons of AMS-02 for the electron channel. Dark matter with mass below a few GeV gets excluded by the cosmic-ray positrons of AMS-02 for the electron, muon and tau channels.

Confining a bi-enzyme inside the nanochannels of a porous aluminum oxide membrane for accelerating the enzymatic reactions

An artificial metabolon with high conversion efficiency was constructed by confining a bi-enzyme into porous aluminum oxide nanochannels, which accelerated enzymatic reactions by minimizing the diffusion loss of intermediate species.

The effect of diffusion loss on the time-varying giant Panda population

It has been certificated that corridors can help giant pandas to keep their habitat from fragmenting. However there are still losses during the process of moving along corridors. In this study, a mathematical model with Allee effect is carried out to describe the diffusion of giant pandas between n patches. Some criteria are obtained to keep the system persisting. It is proved that the system has a unique positive [Formula: see text]-periodic solution which is globally asymptotically stable. The ecological meanings of these findings are discussed following the results. And some numerical simulations in the Qinling Mountain giant panda nature reservation area are also presented in the end.

Characteristics of size distributions at urban and rural locations in New York

Paired nano- and long-tube Scanning Mobility Particle Sizer (SMPS) systems were operated for four different intensive field campaigns in New York State. Two of these campaigns were at Queens College in New York City, during the summer of 2001 and the winter of 2004. The other field campaigns were at rural sites in New York State. The data with the computed diffusion loss corrections for the sampling lines and the SMPS instruments were examined and the combined SMPS data sets for each campaign were obtained. The diffusion corrections significantly affect total number concentrations, and in New York City, affect the mode structure of the size distributions. The relationship between merged and integrated SMPS total number concentrations with the diffusion loss corrections and the CPC number concentrations yield statistically significant increases (closer to 1) in the slope and correlation coefficient compared to the uncorrected values. The measurements are compared to PM2.5 mass concentrations and ion balance indications of aerosol acidity. Analysis of particle growth rate in comparison to other observations can classify the events and illustrate that urban and rural new particle formation and growth are the result of different causes. Periods of low observed PM2.5 mass, high number concentration, and low median diameter due to small fresh particles are associated with primary emissions for the urban sites; and with particle nucleation and growth for the rural sites. The observations of high PM2.5 mass, lower number concentrations, and higher median diameter are mainly due to an enhancement of photochemical reactions leading to condensation processes in relatively aged air. There are statistically different values for the condensation sink (CS) between urban and rural areas. While there is good association (r2>0.5) between the condensation sink (CS) in the range of 8.35–283.9 nm and PM2.5 mass in the urban areas, there is no discernable association in the rural areas. The average values computed for the CS lie in the range 8.7×10−3–3.5×10−2 s−1.

Characteristics of size distributions at urban and rural locations in New York

Paired nano- and long-tube Scanning Mobility Particle Sizer (SMPS) systems were operated for four different intensive field campaigns in New York State. Two of these campaigns were at Queens College in New York City, during the summer of 2001 and the winter of 2004. The other field campaigns were at rural sites in New York State. The data with the computed diffusion loss corrections for the sampling lines and the SMPS instruments were examined and the combined SMPS data sets for each campaign were obtained. The diffusion corrections significantly affect total number concentrations, and in New York City, affect the mode structure of the size distributions. The relationship between merged and integrated SMPS total number concentrations with the diffusion loss corrections and the CPC number concentrations yield statistically significant increases (closer to 1) in the slope and correlation coefficient compared to the uncorrected values. The measurements are compared to PM2.5 mass concentrations and ion balance indications of aerosol acidity. Periods of low observed PM2.5 mass, high number concentration, and low median diameter due to small fresh particles are associated with primary emissions for the urban sites; and with particle nucleation and growth for the rural sites. The observations of high PM2.5 mass, lower number concentrations, and higher median diameter are mainly due to an enhancement of coagulation and/or condensation processes in relatively aged air. There are statistically different values for the condensation sink (CS) between urban and rural areas. While there is good association (r2>0.5) between the condensation sink (CS) in the range of 8.35–283.9 nm and PM2.5 mass in the urban areas, there is no discernable association in the rural areas. The average (±standard deviation) of CS lies in the range 6.5(±3.3)×10−3–2.4(±0.9)×10−2.

Anomalous Out-Diffusion Profiles of Nitrogen in Silicon

Out-diffusion nitrogen profiles measured by SIMS after annealing at 850 and 800oC, have a peculiar minimum at a depth of about 5 m. The profiles are well reproduced by simulations assuming that there is a considerable fraction of nitrogen stored in substitutional clusters VN4. Upon annealing, these clusters lose nitrogen and convert into a stable high-temperature form VN1. This reaction involves a preliminary attachment of a fast-diffusing interstitial trimer, N3. Accordingly, the conversion occurs only in the bulk but not at the surface (due to out-diffusion loss of N3), and the substitutional component decreases from the surface towards the bulk. By fitting the profiles, the two basic parameters of the N2/N1 transport are deduced: P = D1K1/2 (a combination of the monomeric diffusivity D1 and the dissociation constant of dimers, K), and the dissociation time of dimers. With these data, D1(T) and K(T) are specified.

The Study of Guide Vanes on Submersible Pump

Because the structure of submersible pump is special, and common guide vane is a factor effecting low efficiency, those guide vanes design method is different from ones of common axial flow pump and mixed flow pump. This paper introduces the design methods of guide vane on submersible pump. To improve the total performance, submersible pump structure, hydraulic performance, diffusion and friction loss are considered comprehensively when the meridian plane of guide vane is designed. The coefficient of diffusion on meridian plane should be larger than the recommended value and limited to avoid heavy flow separation. The guide vane number is bigger and meridian length of guide vane is shortened. For example, the number of guide vane can be nine or eleven, even thirteen when impeller blade number is four. Bigger number of guide vane makes the short guide vane placed on smaller diameter and avoids flow passage diffused more. On the other hand, smaller diameter will decrease pump dimension, weight, and production cost. To Balance the recycled energy and loss energy, outlet angle of guide vane should be reduced suitable. The angle should be 90 degree if completely recycling the rotating flow energy, but outlet angle should be larger than 90 degree if considering finite cascade. Those two angles will bring large diffusion of flow passage, large diffusion loss and flow friction force. Since the diffusion loss counts heavier percent of hydraulic loss, the angle should be reduced, such as 70 degree. That smaller angle doesn’t recycle completely the rotating energy, but hydraulic loss is decreased, and the efficiency of pump is higher instead. The test testifies that the efficiency of submersible pump designed by those above measures can reach 88%.