11,821 research outputs found
Irreversibility of field-induced magnetostructural transition in NiCoMnSb shape memory alloy revealed by magnetization, transport and heat capacity studies
The effects of magnetic field on the martensitic transition have been studied
in Ni45Co5Mn38Sb12. We find a large field-induced irreversibility in this
system, as revealed by the field dependence of resistivity, magnetization, and
heat capacity data. At the critical temperature, the field-induced conversion
of the martensitic to austenite phase is not reversible under any field
variation. At this temperature any energy fluctuation induces nucleation and
growth of the equilibrium austenite phase at the expense of the metastable
martensitic phase and gets arrested. All these three measurements completely
rule out the coexistence of austenite and martensitic phases in the
irreversibility regime.Comment: 13 pages, 4 figure
Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy
The effect of pressure on the magnetic and the magnetocaloric properties
around the martensitic transformation temperature in NiCoMnSb Heusler alloy has
been studied. The martensitic transition temperature has significantly shifted
to higher temperatures with pressure, whereas the trend is opposite with the
application of applied magnetic field. The maximum magnetic entropy change
around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg
K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by
adjusting the Co concentration and applying suitable pressure, NiCoMnSb system
can be tuned to achieve giant magnetocaloric effect spread over a large
temperature span around the room temperature, thereby making it a potential
magnetic refrigerant material for applications.Comment: 16 pages, 5 figure
Star Clusters in the Magellanic Clouds-1: Parameterisation and Classification of 1072 Clusters in the LMC
We have introduced a semi-automated quantitative method to estimate the age
and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using
the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study
brings out 308 newly parameterised clusters. In a first of its kind, the LMC
clusters are classified into groups based on richness/mass as very poor, poor,
moderate and rich clusters, similar to the classification scheme of open
clusters in the Galaxy. A major cluster formation episode is found to happen at
125 +- 25 Myr in the inner LMC. The bar region of the LMC appears prominently
in the age range 60 - 250 Myr and is found to have a relatively higher
concentration of poor and moderate clusters. The eastern and the western ends
of the bar are found to form clusters initially, which later propagates to the
central part. We demonstrate that there is a significant difference in the
distribution of clusters as a function of mass, using a movie based on the
propagation (in space and time) of cluster formation in various groups. The
importance of including the low mass clusters in the cluster formation history
is demonstrated. The catalog with parameters, classification, and cleaned and
isochrone fitted CMDs of 1072 clusters, which are available as online material,
can be further used to understand the hierarchical formation of clusters in
selected regions of the LMC.Comment: 19 pages, 19figures, published in MNRAS on August 16, 2016
Supplementary material is available in the MNRAS websit
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R-PEKS: RBAC Enabled PEKS for Secure Access of Cloud Data
In the recent past, few works have been done by combining attribute-based access control with multi-user PEKS, i.e., public key encryption with keyword search. Such attribute enabled searchable encryption is most suitable for applications where the changing of privileges is done once in a while. However, to date, no efficient and secure scheme is available in the literature that is suitable for these applications where changing privileges are done frequently. In this paper our contributions are twofold. Firstly, we propose a new PEKS scheme for string search, which, unlike the previous constructions, is free from bi-linear mapping and is efficient by 97% compared to PEKS for string search proposed by Ray et.al in TrustCom 2017. Secondly, we introduce role based access control (RBAC) to multi-user PEKS, where an arbitrary group of users can search and access the encrypted files depending upon roles. We termed this integrated scheme as R-PEKS. The efficiency of R-PEKS over the PEKS scheme is up to 90%. We provide formal security proofs for the different components of R-PEKS and validate these schemes using a commercial dataset
Production and Equilibration of the Quark-Gluon Plasma with Chromoelectric Field and Minijets
Production and equilibration of quark-gluon plasma are studied within the
color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic
transport equations for quarks, antiquarks and gluons, are solved in the
extended phase space which includes coordinates, momenta and color. Before the
chromoelectric field is formed, hard and semihard partons are produced via
minijets which provide the initial conditions necessary to solve the transport
equations. The model predicts that in spite of the vast difference between the
RHIC and LHC incident energies, once the local equilibrium is reached, the
energy densities, the number densities and the temperatures at the two machines
may not be very different from each other. The minijet input significantly
alters the evolution of the deconfined matter, unless the color field is too
strong. For the input parameters used here the equilibration time is estimated
to be fm at RHIC and fm at LHC, measured from the instant
when the two colliding nuclei have just passed through each other. The
temperature at equilibration is found to be MeV at RHIC and MeV at LHC.Comment: version to appear in Phys. Rev. C; discussion enlarged to include
comparison with other models; conclusions unchanged; 14 single-spaced pages +
8 ps figure
Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys
The effect of Co on the structural, magnetic and magnetocaloric effect (MCE)
of Ni50-xCoxMn38Sb12 (x=0,2,3,4,5) Heusler alloys was studied. Using x-ray
diffraction, we show the evolution of the martensitic phase from the austenite
phase. The martensitic transition temperature is found to decrease
monotonically with Co concentration. Remarkable enhancement of MCE is observed
near room temperature upon Co substitution. The maximum magnetic entropy change
of 34 Jkg-1K-1 was achieved in x=5 at 262 K in a field of 50 kOe and a value of
29 Jkg-1K-1 found near room temperature. The significant increase in the
magnetization associated with the reverse martensitic transition is responsible
for the giant MCE in these compounds.Comment: 14 pages, 5 figure
Observation of enhanced exchange bias behavior in NiCoMnSb Heusler alloys
We report the observation of large exchange bias in Ni50-xCoxMn38Sb12 Heusler
alloys with x=0, 2, 3, 4, 5, which is attributed to the coexistence of
ferromagnetic and antiferromagnetic phases in the martensitic phase. The phase
coexistence is possibly due to the supercooling of the high temperature
ferromagnetic phase and the predominant antiferromagnetic component in the
martensitic phase. The presence of exchange bias is well supported by the
observation of training effect. The exchange bias field increases with Co
concentration. The maximum value of 480 Oe at T=3K is observed in x=5 after
field cooling in 50 kOe, which is almost double the highest value reported so
far in any Heusler alloy system. Increase in the antiferromagnetic coupling
after Co substitution is found to be responsible for the increase in the
exchange bias.Comment: 17 pages, 8 figure
Correlation between stick-slip frictional sliding and charge transfer
A decade ago, Budakian and Putterman (Phys. Rev. Lett., {\bf 85}, 1000
(2000)) ascribed friction to the formation of bonds arising from contact
charging when a gold tip of a surface force apparatus was dragged on
polymethylmethacrylate surface. We propose a stick-slip model that captures the
observed correlation between stick-slip events and charge transfer, and the
lack of dependence of the scale factor connecting the force jumps and charge
transfer on normal load. Here, stick-slip dynamics arises as a competition
between the visco-elastic and plastic deformation time scales and that due to
the pull speed with contact charging playing a minor role. Our model provides
an alternate basis for explaining most experimental results without ascribing
friction to contact charging.Comment: 8 pages, 4 figures, To be appeared in Physical Review
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