9,869 research outputs found
Properties of neutral mesons in a hot and magnetized quark matter
The properties of non-interacting and mesons are studied
at finite temperature, chemical potential and in the presence of a constant
magnetic field. To do this, the energy dispersion relations of these particles,
including nontrivial form factors, are derived using a derivative expansion of
the effective action of a two-flavor, hot and magnetized Nambu--Jona-Lasinio
(NJL) model up to second order. The temperature dependence of the pole and
screening masses as well as the directional refraction indices of magnetized
neutral mesons are explored for fixed magnetic fields and chemical potentials.
It is shown that, because of the explicit breaking of the Lorentz invariance by
the magnetic field, the refraction index and the screening mass of neutral
mesons exhibit a certain anisotropy in the transverse and longitudinal
directions with respect to the direction of the external magnetic field. In
contrast to their longitudinal refraction indices, the transverse indices of
the neutral mesons are larger than unity.Comment: V1: 26 pages, 15 figures; V2: Discussions improved, references added.
Version accepted for publication in PR
Interplay of size and Landau quantizations in the de Haas-van Alphen oscillations of metallic nanowires
We examine the interplay between size quantization and Landau quantization in
the De Haas-Van Alphen oscillations of clean, metallic nanowires in a
longitudinal magnetic field for `hard' boundary conditions, i.e. those of an
infinite round well, as opposed to the `soft' parabolically confined boundary
conditions previously treated in Alexandrov and Kabanov (Phys. Rev. Lett. {\bf
95}, 076601 (2005) (AK)). We find that there exist {\em two} fundamental
frequencies as opposed to the one found in bulk systems and the three
frequencies found by AK with soft boundary counditions. In addition, we find
that the additional `magic resonances' of AK may be also observed in the
infinite well case, though they are now damped. We also compare the numerically
generated energy spectrum of the infinite well potential with that of our
analytic approximation, and compare calculations of the oscillatory portions of
the thermodynamic quantities for both models.Comment: Title changed, paper streamlined on suggestion of referrees, typos
corrected, numerical error in figs 2 and 3 corrected and final result
simplified -- two not three frequencies (as in the previous version) are
observed. Abstract altered accordingly. Submitted to Physical Review
Chiral density waves in quark matter within the Nambu--Jona-Lasinio model in an external magnetic field
A possibility of formation of static dual scalar and pseudoscalar density
wave condensates in dense quark matter is considered for the
Nambu--Jona-Lasinio model in an external magnetic field. Within a mean-field
approximation, the effective potential of the theory is obtained and its minima
are numerically studied; a phase diagram of the system is constructed. It is
shown that the presence of a magnetic field favors the formation of spatially
inhomogeneous condensate configurations at low temperatures and arbitrary
non-zero values of the chemical potential.Comment: 13 pages, 4 figure
Phase diagram of hot magnetized two-flavor color superconducting quark matter
A two-flavor color superconducting (2SC) Nambu--Jona-Lasinio (NJL) model is
introduced at finite temperature T, chemical potential mu and in the presence
of a constant magnetic field eB. The effect of (T,mu,eB) on the formation of
chiral and color symmetry breaking condensates is studied. The complete phase
portrait of the model in T-mu, mu-eB, and T-eB phase spaces for various fixed
eB, T, and mu is explored. A threshold magnetic field eB_t~ 0.5 GeV^2 is found
above which the dynamics of the system is solely dominated by the lowest Landau
level (LLL) and the effects of T and mu are partly compensated by eB.Comment: V1: 29 pages, 15 figures, 3 tables. V2: Discussions improved. Version
accepted for publication in PR
Heritable functional architecture in human visual cortex
How much of the functional organization of our visual system is inherited? Here we tested the heritability of retinotopic maps in human visual cortex using functional magnetic resonance imaging. We demonstrate that retinotopic organization shows a closer correspondence in monozygotic (MZ) compared to dizygotic (DZ) twin pairs, suggesting a partial genetic determination. Using population receptive field (pRF) analysis to examine the preferred spatial location and selectivity of these neuronal populations, we estimate a heritability around 10–20% for polar angle preferences and spatial selectivity, as quantified by pRF size, in extrastriate areas V2 and V3. Our findings are consistent with heritability in both the macroscopic arrangement of visual regions and stimulus tuning properties of visual cortex. This could constitute a neural substrate for variations in a range of perceptual effects, which themselves have been found to be at least partially genetically determined. These findings also add convergent evidence for the hypothesis that functional map topology is linked with cortical morphology
Teachers' Professional Identity in the Context of School-based Sexuality Education in Uganda - a Qualitative Study
School-based sexuality education makes teachers important gatekeepers of students’ access
to information about sexual and reproductive
health and rights. The school setting has the
potential to reach large numbers of students.
However, teachers’ professional identities may
go beyond, differ from or even conflict with the
qualities required of sexuality educators.
To gain a better understanding of the role of
professional identity in the delivery of schoolbased sexuality education, this study used
cultural schema theory to study teachers’ professional identities, and how these motivate
them to provide sexuality education. In-depth
interviews were conducted with 40 sexuality
education teachers at secondary schools in
Kampala, the capital of Uganda. Sexuality
education lessons were observed to validate the
findings from the interviews. Results identified
five cultural schemas of professional identity:
(i) upholder of ethics and regulations;
(ii) authority figure; (iii) counsellor and guide;
(iv) role model; and (v) guardian. The study
concludes that teachers’ cultural schemas of
professional identity motivate them to adhere
to moral discourses of abstinence and sexual
innocence. To support teachers in taking
more comprehensive approaches to sexuality
education, it is important that they receive
adequate teacher training and support from
the Ugandan government, the school
administration and the wider communit
Young people’s perceptions of relationships and sexual practices in the abstinence-only context of Uganda
The Ugandan government has been criticised on several grounds for its
abstinence-only policies on sexuality education directed towards young
people. These grounds include the failure to recognise the multiple
realities faced by young people, some of whom may already be sexually
active. In the study reported on this paper, students’ perceptions
of relationships and sexual practices were analysed to obtain an
understanding of how young people construct and negotiate their
sexual agency in the context of abstinence-only messages provided
in Ugandan secondary schools and at the wider community level. Ten
in-depth interviews and six focus group discussions were conducted
with students aged 15–19 years (N = 55) at an urban co-educational
secondary school. Data were transcribed verbatim and analysed using
grounded theory. Findings show that students engage in sexual activity
despite their belief that contraception is ineffective and their fears for
the consequences. Students’ age, gender, financial capital and perceived
sexual desire further increase risk and vulnerability. To improve their
effectiveness, school-based sexuality education programmes should
support students to challenge and negotiate structural factors such as
gender roles and sociocultural norms that influence sexual practices
and increase vulnerability and risk
Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model
Infrared to millimetre spectral energy distributions have been obtained for
41 bright ultra-luminous infrared galaxies. The observations were carried out
with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with
SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources
were observed at 1.2 and 2.2 m with the 2.2 m telescope on Calar Alto.
These new SEDs represent the most complete set of infrared photometric
templates obtained so far on ULIRGs in the local universe.Comment: 23 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Modified Zakharov equations for plasmas with a quantum correction
Quantum Zakharov equations are obtained to describe the nonlinear interaction
between quantum Langmuir waves and quantum ion-acoustic waves. These quantum
Zakharov equations are applied to two model cases, namely the four-wave
interaction and the decay instability. In the case of the four-wave
instability, sufficiently large quantum effects tend to suppress the
instability. For the decay instability, the quantum Zakharov equations lead to
results similar to those of the classical decay instability except for quantum
correction terms in the dispersion relations. Some considerations regarding the
nonlinear aspects of the quantum Zakharov equations are also offered.Comment: 4 figures. Accepted for publication in Physics of Plasmas (2004
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