698 research outputs found
Quark deconfinement in neutron star cores: The effects of spin-down
We study the role of spin-down in driving quark deconfinement in the high
density core of isolated neutron stars. Assuming spin-down to be solely due to
magnetic braking, we obtain typical timescales to quark deconfinement for
neutron stars that are born with Keplerian frequencies. Employing different
equations of state (EOS), we determine the minimum and maximum neutron star
masses that will allow for deconfinement via spin-down only. We find that the
time to reach deconfinement is strongly dependent on the magnetic field and
that this time is least for EOS that support the largest minimum mass at zero
spin, unless rotational effects on stellar structure are large. For a fiducial
critical density of for the transition to the quark phase
(g/cm is the saturation density of nuclear
matter), we find that neutron stars lighter than cannot reach a
deconfined phase. Depending on the EOS, neutron stars of more than
can enter a quark phase only if they are spinning faster than
about 3 milliseconds as observed now, whereas larger spin periods imply that
they are either already quark stars or will never become one.Comment: 4 pages, 4 figures, submitted to ApJ
Magnetism of Two Coupled Harmonic Oscillators
The thermodynamical properties of a system of two coupled harmonic
oscillators in the presence of an uniform magnetic field B are investigated.
Using an unitary transformation, we show that the system can be diagonalized in
simple way and then obtain the energy spectrum solutions. These will be used to
determine the thermodynamical potential in terms of different physical
parameters like the coupling parameter \alpha. This allows us to give a
generalization of already significant published work and obtain different
results, those could be used to discuss the magnetism of the system. Different
limiting cases, in terms of \alpha and B, have been discussed. In fact, quantum
corrections to the Landau diamagnetism and orbital paramagnetism are found.Comment: 25 page
Periodic Structures with Rashba Interaction in Magnetic Field
We analyze the behaviour of a system of particles living on a periodic
crystal in the presence of a magnetic field B. This can be done by involving a
periodic potential U(x) and the Rashba interaction of coupling constant k_{so}.
By resorting the corresponding spectrum, we explicitly determine the band
structures and the Bloch spinors. These allow us to discuss the system
symmetries in terms of the polarizations where they are shown to be broken. The
dynamical spin will be studied by calculating different quantities. In the
limits: k_{so} and U(x)=0, we analyze again the system by deriving different
results. Considering the strong case, we obtain an interesting result that
is the conservation of the polarizations. Analyzing the critical point
\lambda_{k,\sigma}=\pm\sq{1\over 2}, we show that the Hilbert space associated
to the spectrum in z-direction has a zero mode energy similar to that of
massless Dirac fermions in graphene. Finally, we give the resulting energy
spectrum when B=0 and U(x) is arbitrary.Comment: 24 pages, references added, misprints corrected. Version to appear in
JP
United Nations Educational Scientific and Cultural Organization and International Atomic Energy Agency THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS SOLVING THE GENERAL TRUNCATED MOMENT PROBLEM BY r-GENERALIZED FIBONACCI SEQUENCES METHOD
Abstract We give in this paper a new method for solving the generalized truncated power moment problem. To this aim we use r-generalized Fibonacci sequences and their associated minimal polynomials. We provide an algorithm of construction of solutions in a short method. This method allows us to avoid any appeal to Hankel matrices or any positive difiniteness conditions as in Flessas-Burton-Whitehead (FBW) approach. Examples and general cases are discussed
Assessing indicators of runoff and erosion by rain simulation in the Ben Ahmed watershed (Central Morocco)
The objective of this study was to investigate the risks of runoff and erosion of soils in the Ben Ahmed watershed, it's located in the region of casa-settat, 70 km south-east of Casablanca, and characterized by a semi-arid climate. The study consists of measuring on 1 m2 plot, the volumes of runoff and sediments, under the influence of rainfall generation (60mm/30 min). Soil samples were collected from each plot to determine texture, organic matter and humidity. Results obtained show that the detachability varies between 19 and 34 g/l, infiltrability oscillate between 15 and 37 mm.h-. Pearson correlation test shows that infiltration was negatively correlated with runoff and soil detachability (R=-0.99, R=-0.87 respectively). Itâs significantly correlated with the proportions of sand(R=0.69), silt (R= -0.98) an clay (R= 0.92), however, is weakly correlated with organic matter (R=-0.32). Infiltration and detachability were significantly correlated with humidity (R = -0.99, R = -0.63respectively)
Machine-Learning Approach to Determine Surface Quality on a Reactor Pressure Vessel (RPV) Steel
Surface quality measures such as roughness, and especially its uncertain character, affect most magnetic non-destructive testing methods and limits their performance in terms of an achievable signal-to-noise ratio and reliability. This paper is primarily focused on an experimental study targeting nuclear reactor materials manufactured from the milling process with various machining parameters to produce varying surface quality conditions to mimic the varying material surface qualities of in-field conditions. From energising a local area electromagnetically, a receiver coil is used to obtain the emitted Barkhausen noise, from which the condition of the material surface can be inspected. Investigations were carried out with the support of machine-learning algorithms, such as Neural Networks (NN) and Classification and Regression Trees (CART), to identify the differences in surface quality. Another challenge often faced is undertaking an analysis with limited experimental data. Other non-destructive methods such as Magnetic Adaptive Testing (MAT) were used to provide data imputation for missing data using other intelligent algorithms. For data reinforcement, data augmentation was used. With more data the problem of âthe curse of data dimensionalityâ is addressed. It demonstrated how both data imputation and augmentation can improve measurement datasets
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Development of Thiophene Compounds as Potent Chemotherapies for the Treatment of Cutaneous Leishmaniasis Caused by Leishmania major
Leishmania major (L. major) is a protozoan parasite that causes cutaneous leishmaniasis. About 12 million people are currently infected with an annual incidence of 1.3 million cases. The purpose of this study was to synthesize a small library of novel thiophene derivatives, and evaluate its parasitic activity, and potential mechanism of action (MOA). We developed a structureâactivity relationship (SAR) study of the thiophene molecule 5A. Overall, eight thiophene derivatives of 5A were synthesized and purified by silica gel column chromatography. Of these eight analogs, the molecule 5D showed the highest in vitro activity against Leishmania major promastigotes (EC50 0.09 ± 0.02 ”M), with an inhibition of the proliferation of intracellular amastigotes higher than 75% at only 0.63 ”M and an excellent selective index. Moreover, the effect of 5D on L. major promastigotes was associated with generation of reactive oxygen species (ROS), and in silico docking studies suggested that 5D may play a role in inhibiting trypanothione reductase. In summary, the combined SAR study and the in vitro evaluation of 5A derivatives allowed the identification of the novel molecule 5D, which exhibited potent in vitro anti-leishmanial activity resulting in ROS production leading to cell death with no significant cytotoxicity towards mammalian cells
2-Methyl-3-(n-octylsulfanÂyl)quinoxaline
All the non-H atoms of the title compound, C17H24N2S, lie almost in a common plane (r.m.s. deviation = 0.049â
Ă
). The octyl chain adopts an all-trans conformation
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