1,150 research outputs found
Magnetocaloric effect near room temperature in quintenary and sextenary Heusler alloys
An inverse magnetocaloric effect is studied in Ni2Mn1+xX1-x-type Heusler alloys. Principally known for their shape-memory properties, these alloys also exhibit significant entropy and temperature changes (ΔS and ΔTAd, respectively) under adiabatic conditions when a modest magnetic field is applied. We investigated the impact on magnetocaloric properties of introducing substantial chemical disorder on the X-site (X = Si, Ga, In), of replacing Ni with nonmagnetic Ag, and of replacing a small amount of Mn with Gd. While a reduction in ΔS is observed in the first two cases, we observe a significant enhancement of ΔS when a small amount of Gd is substituted for Mn. A thermodynamic analysis was conducted using magnetization and heat capacity data to estimate adiabatic temperature changes in the range of ΔTAd ≃ -1 to -3 K for a 5 T magnetic field. Several alloys characterized in this study exhibit these respectable ΔTAd values near room temperature, making them potentially viable candidates for magnetic refrigeration applications
Investigation of double beta decay with the NEMO-3 detector
The double beta decay experiment NEMO~3 has been taking data since February
2003. The aim of this experiment is to search for neutrinoless
() decay and investigate two neutrino double beta decay in
seven different isotopically enriched samples (Mo, Se,
Ca, Zr, Cd, Te and Nd). After analysis of
the data corresponding to 3.75 y, no evidence for decay in the
Mo and Se samples was found. The half-life limits at the 90%
C.L. are y and y, respectively.
Additionally for decay the following limits at the 90% C.L.
were obtained, y for Ca, y
for Zr and y for Nd. The
decay half-life values were precisely measured for all investigated isotopes.Comment: 12 pages, 4 figures, 5 tables; talk at conference on "Fundamental
Interactions Physics" (ITEP, Moscow, November 23-27, 2009
Studying the Lunar-Solar Wind Interaction with the SARA Experiment aboard the Indian Lunar Mission Chandrayaan-1
The first Indian lunar mission Chandrayaan-1 was launched on 22 October 2008.
The Sub-keV Atom Reflecting Analyzer (SARA) instrument onboard Chandrayaan-1
consists of an energetic neutral atom (ENA) imaging mass analyzer called CENA
(Chandrayaan-1 Energetic Neutrals Analyzer), and an ion-mass analyzer called
SWIM (Solar wind Monitor). CENA performed the first ever experiment to study
the solar wind-planetary surface interaction via detection of sputtered neutral
atoms and neutralized backscattered solar wind protons in the energy range
~0.01-3.0 keV. SWIM measures solar wind ions, magnetosheath and magnetotail
ions, as well as ions scattered from lunar surface in the ~0.01-15 keV energy
range. The neutral atom sensor uses conversion of the incoming neutrals to
positive ions, which are then analyzed via surface interaction technique. The
ion mass analyzer is based on similar principle. This paper presents the SARA
instrument and the first results obtained by the SWIM and CENA sensors. SARA
observations suggest that about 20% of the incident solar wind protons are
backscattered as neutral hydrogen and ~1% as protons from the lunar surface.
These findings have important implications for other airless bodies in the
solar system.Comment: 4 pages, 6 figure
Spectral Representation for the Effective Macroscopic Response of a Polycrystal: Application to Third-Order Nonlinear Susceptibility
Erratum:
In our paper, we show that the spectral representation for isotropic
two-component composites also applies to uniaxial polycrystals. We have learned
that this result was, in fact, first conjectured by G.W. Milton. While our
derivation is more detailed, our result for the spectral function is the same
as Milton's. We very much regret not having been aware of this work at the time
of writing our paper.
Original abstract:
We extend the spectral theory used for the calculation of the effective
linear response functions of composites to the case of a polycrystalline
material with uniaxially anisotropic microscopic symmetry. As an application,
we combine these results with a nonlinear decoupling approximation as modified
by Ma et al., to calculate the third-order nonlinear optical susceptibility of
a uniaxial polycrystal, assuming that the effective dielectric function of the
polycrystal can be calculated within the effective-medium approximation.Comment: v2 includes erratum and the original preprin
A simple high-sensitivity technique for purity analysis of xenon gas
We report on the development and performance of a high-sensitivity
purity-analysis technique for gaseous xenon. The gas is sampled at macroscopic
pressure from the system of interest using a UHV leak valve. The xenon present
in the sample is removed with a liquid-nitrogen cold trap, and the remaining
impurities are observed with a standard vacuum mass-spectroscopy device. Using
calibrated samples of xenon gas spiked with known levels of impurities, we find
that the minimum detectable levels of N2, O2, and methane are 1 ppb, 160 ppt,
and 60 ppt respectively. This represents an improvement of about a factor of
10,000 compared to measurements performed without a coldtrap.Comment: 20 pages, 5 figure
Double beta decay: present status
The present status of double beta decay experiments (including the search for
, EC and ECEC processes) are reviewed. The results of
the most sensitive experiments are discussed. Average and recommended half-life
values for two-neutrino double beta decay are presented. Conservative upper
limits on effective Majorana neutrino mass and the coupling constant of the
Majoron to the neutrino are established as eV and , respectively. Proposals for future double beta decay
experiments with a sensitivity for the at the level of (0.01-0.1)
eV are considered.Comment: 33 pages included 7 figures and 14 tables; an extended version of the
invited talk at 13th Lomonosov Conference of Elementary Particle Physics,
23-29 August, 2007, Moscow, Russi
Measurement of double beta decay of 100Mo to excited states in the NEMO 3 experiment
The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru
is studied using the NEMO 3 data. After the analysis of 8024 h of data the
half-life for the two-neutrino double beta decay of 100Mo to the excited 0^+_1
state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x
10^20 y. The signal-to-background ratio is equal to 3. Information about energy
and angular distributions of emitted electrons is also obtained. No evidence
for neutrinoless double beta decay to the excited 0^+_1 state has been found.
The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y
(at 90% C.L.).
The search for the double beta decay to the 2^+_1 excited state has allowed
the determination of limits on the half-life for the two neutrino mode
T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the
neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).Comment: 23 pages, 7 figures, 4 tables, submitted to Nucl. Phy
Effect of deformation on two-neutrino double beta decay matrix elements
We study the effect of deformation on the two-neutrino double beta decay for
ground state to ground state transitions in all the nuclei whose half-lives
have been measured. Our theoretical framework is a deformed QRPA based in
Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same
time the main characteristics of the two single beta branches, as well as the
double beta matrix elements. We find a suppression of the double beta matrix
element with respect to the spherical case when the parent and daughter nuclei
have different deformations
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