144 research outputs found
Role of domain walls in the abnormal photovoltaic effect in BiFeO3
Recently, the anomalous photovoltaic (PV) effect in BiFeO3 (BFO) thin
films, which resulted in open circuit voltages (V-oc) considerably
larger than the band gap of the material, has generated a revival of the
entire field of photoferroelectrics. Here, via temperature-dependent PV
studies, we prove that the bulk photovoltaic (BPV) effect, which has
been studied in the past for many non-centrosymmetric materials, is at
the origin of the anomalous PV effect in BFO films. Moreover, we show
that irrespective of the measurement geometry, V-oc as high as 50V can
be achieved by controlling the conductivity of domain walls (DW). We
also show that photoconductivity of the DW is markedly higher than in
the bulk of BFO
Energy-Sensitive and "Classical-like" Distances Between Quantum States
We introduce the concept of the ``polarized'' distance, which distinguishes
the orthogonal states with different energies. We also give new inequalities
for the known Hilbert-Schmidt distance between neighbouring states and express
this distance in terms of the quasiprobability distributions and the normally
ordered moments. Besides, we discuss the distance problem in the framework of
the recently proposed ``classical-like'' formulation of quantum mechanics,
based on the symplectic tomography scheme. The examples of the Fock, coherent,
``Schroedinger cats,'' squeezed, phase, and thermal states are considered.Comment: 23 pages, LaTex, 2 eps figures, to appear in Physica Script
Analytic results for Gaussian wave packets in four model systems: II. Autocorrelation functions
The autocorrelation function, A(t), measures the overlap (in Hilbert space)
of a time-dependent quantum mechanical wave function, psi(x,t), with its
initial value, psi(x,0). It finds extensive use in the theoretical analysis and
experimental measurement of such phenomena as quantum wave packet revivals. We
evaluate explicit expressions for the autocorrelation function for
time-dependent Gaussian solutions of the Schrodinger equation corresponding to
the cases of a free particle, a particle undergoing uniform acceleration, a
particle in a harmonic oscillator potential, and a system corresponding to an
unstable equilibrium (the so-called `inverted' oscillator.) We emphasize the
importance of momentum-space methods where such calculations are often more
straightforwardly realized, as well as stressing their role in providing
complementary information to results obtained using position-space
wavefunctions.Comment: 18 pages, RevTeX, to appear in Found. Phys. Lett, Vol. 17, Dec. 200
A Profile Likelihood Analysis of the Constrained MSSM with Genetic Algorithms
The Constrained Minimal Supersymmetric Standard Model (CMSSM) is one of the
simplest and most widely-studied supersymmetric extensions to the standard
model of particle physics. Nevertheless, current data do not sufficiently
constrain the model parameters in a way completely independent of priors,
statistical measures and scanning techniques. We present a new technique for
scanning supersymmetric parameter spaces, optimised for frequentist profile
likelihood analyses and based on Genetic Algorithms. We apply this technique to
the CMSSM, taking into account existing collider and cosmological data in our
global fit. We compare our method to the MultiNest algorithm, an efficient
Bayesian technique, paying particular attention to the best-fit points and
implications for particle masses at the LHC and dark matter searches. Our
global best-fit point lies in the focus point region. We find many
high-likelihood points in both the stau co-annihilation and focus point
regions, including a previously neglected section of the co-annihilation region
at large m_0. We show that there are many high-likelihood points in the CMSSM
parameter space commonly missed by existing scanning techniques, especially at
high masses. This has a significant influence on the derived confidence regions
for parameters and observables, and can dramatically change the entire
statistical inference of such scans.Comment: 47 pages, 8 figures; Fig. 8, Table 7 and more discussions added to
Sec. 3.4.2 in response to referee's comments; accepted for publication in
JHE
Isothermal Microcalorimetry, a New Tool to Monitor Drug Action against Trypanosoma brucei and Plasmodium falciparum
Isothermal microcalorimetry is an established tool to measure heat flow of physical, chemical or biological processes. The metabolism of viable cells produces heat, and if sufficient cells are present, their heat production can be assessed by this method. In this study, we investigated the heat flow of two medically important protozoans, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Heat flow signals obtained for these pathogens allowed us to monitor parasite growth on a real-time basis as the signals correlated with the number of viable cells. To showcase the potential of microcalorimetry for measuring drug action on pathogenic organisms, we tested the method with three antitrypanosomal drugs, melarsoprol, suramin and pentamidine and three antiplasmodial drugs, chloroquine, artemether and dihydroartemisinin, each at two concentrations on the respective parasite. With the real time measurement, inhibition was observed immediately by a reduced heat flow compared to that in untreated control samples. The onset of drug action, the degree of inhibition and the time to death of the parasite culture could conveniently be monitored over several days. Microcalorimetry is a valuable element to be added to the toolbox for drug discovery for protozoal diseases such as human African trypanosomiasis and malaria. The method could probably be adapted to other protozoan parasites, especially those growing extracellularly
Electromagnetic Dissociation as a Tool for Nuclear Structure and Astrophysics
Coulomb dissociation is an especially simple and important reaction
mechanism. Since the perturbation due to the electric field of the (target)
nucleus is exactly known, firm conclusions can be drawn from such measurements.
Electromagnetic matrixelements and astrophysical S-factors for radiative
capture processes can be extracted from experiments. We describe the basic
elements of the theory of nonrelativistic and relativistic electromagnetic
excitation with heavy ions. This is contrasted to electromagnetic excitation
with leptons (electrons), with their small electric charge and the absence of
strong interactions. We discuss various approaches to the study of higher order
electromagnetic effects and how these effects depend on the basic parameters of
the experiment. The dissociation of neutron halo nuclei is studied in a zero
range model using analytical methods. We also review ways how to treat nuclear
interactions, show their characteristics and how to avoid them (as far as
possible). We review the experimental results from a theoretical point of view.
Of special interest for nuclear structure physics is the appearence of low
lying electric dipole strength in neutron rich nuclei. Applications of Coulomb
dissociation to some selected radiative capture reactions relevant for nuclear
astrophysics are discussed. The Coulomb dissociation of 8B is relevant for the
solar neutrino problem. The potential of the method especially for future
investigations of (medium) heavy exotic nuclei for nuclear structure and
astrophysics is explored. We conclude that the Coulomb dissociation mechanism
is theoretically well understood, the potential difficulties are identified and
can be taken care of. Many interesting experiments have been done in this field
and many more are expected in the future.Comment: review article accepted for publication in "Prog. in Part. and Nucl.
Physics", 75 pages, 31 figure
Caffeine Reduces 11β-Hydroxysteroid Dehydrogenase Type 2 Expression in Human Trophoblast Cells through the Adenosine A2B Receptor
Maternal caffeine consumption is associated with reduced fetal growth, but the underlying molecular mechanisms are unknown. Since there is evidence that decreased placental 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) is linked to fetal growth restriction, we hypothesized that caffeine may inhibit fetal growth partly through down regulating placental 11β-HSD2. As a first step in examining this hypothesis, we studied the effects of caffeine on placental 11β-HSD2 activity and expression using our established primary human trophoblast cells as an in vitro model system. Given that maternal serum concentrations of paraxanthine (the primary metabolite of caffeine) were greater in women who gave birth to small-for-gestational age infants than to appropriately grown infants, we also studied the effects of paraxanthine. Our main findings were: (1) both caffeine and paraxanthine decreased placental 11β-HSD2 activity, protein and mRNA in a concentration-dependent manner; (2) this inhibitory effect was mediated by the adenosine A2B receptor, since siRNA-mediated knockdown of this receptor prevented caffeine- and paraxanthine-induced inhibition of placental 11β-HSD2; and (3) forskolin (an activator of adenyl cyclase and a known stimulator of 11β-HSD2) abrogated the inhibitory effects of both caffeine and paraxanthine, which provides evidence for a functional link between exposure to caffeine and paraxanthine, decreased intracellular levels of cAMP and reduced placental 11β-HSD2. Taken together, these findings reveal that placental 11β-HSD2 is a novel molecular target through which caffeine may adversely affect fetal growth. They also uncover a previously unappreciated role for the adenosine A2B receptor signaling in regulating placental 11β-HSD2, and consequently fetal development
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Absence of day-night asymmetry of 862 keV Be-7 solar neutrino rate in Borexino and MSW oscillation parameters
We report on a search for the day-night asymmetry of the Be-7 solar neutrino
rate measured by Borexino at the Laboratori Nazionali del Gran Sasso (LNGS),
Italy. The measured value, Adn=0.001 +- 0.012 (stat) +- 0.007 (syst), shows the
absence of a significant asymmetry. This result alone rejects the so-called LOW
solution at more than 8.5 sigma. Combined with the other solar neutrino data,
it isolates the Large Mixing Angle (LMA) -- MSW solution at DeltaChi2 > 190
without relying on the assumption of CPT symmetry in the neutrino sector. We
also show that including the day-night asymmetry, data from Borexino alone
restricts the MSW neutrino oscillations to the LMA solution at 90% confidence
level.Comment: 5 figures, published on Phys. Lett
Photoproduction of J/psi and of high mass e+e- in ultra-peripheral Au+Au collisions at sqrt(s_NN) = 200 GeV
We present the first measurement of photoproduction of J/psi and of
two-photon production of high-mass e+e- pairs in electromagnetic (or
ultra-peripheral) nucleus-nucleus interactions, using Au+Au data at sqrt(s_NN)
= 200 GeV. The events are tagged with forward neutrons emitted following
Coulomb excitation of one or both Au^{star} nuclei. The event sample consists
of 28 events with m_{e+e-} > 2 GeV/c^2 with zero like-sign background. The
measured cross sections at midrapidity of d\sigma / dy (J/psi + Xn, y=0) = 76
+/- 33 (stat) +/- 11 (syst) micro b and d^2\sigma/dm dy (e^+e^- + Xn, y=0) = 86
+/- 23 (stat) +/- 16 (syst) micro b/(GeV/c^2) for m_{e+e-} \in [2.0,2.8]
GeV/c^2 are consistent with various theoretical predictions.Comment: 345 authors from 52 institutions, 20 pages, 4 figures, 3 tables.
Submitted to Physics Letters B. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
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