12,451 research outputs found
Confinement of two-dimensional excitons in a non-homogeneous magnetic field
The effective Hamiltonian describing the motion of an exciton in an external
non-homogeneous magnetic field is derived. The magnetic field plays the role of
an effective potential for the exciton motion, results into an increment of the
exciton mass and modifies the exciton kinetic energy operator. In contrast to
the homogeneous field case, the exciton in a non-homogeneous magnetic field can
also be trapped in the low field region and the field gradient increases the
exciton confinement. The trapping energy and wave function of the exciton in a
GaAs two-dimensional electron gas for specific circular magnetic field
configurations are calculated. The results show than excitons can be trapped by
non-homogeneous magnetic fields, and that the trapping energy is strongly
correlated with the shape and strength of the non-homogeneous magnetic field
profile.Comment: 9 pages, 12 figure
Exciton trapping in magnetic wire structures
The lateral magnetic confinement of quasi two-dimensional excitons into wire
like structures is studied. Spin effects are take into account and two
different magnetic field profiles are considered, which experimentally can be
created by the deposition of a ferromagnetic stripe on a semiconductor quantum
well with magnetization parallel or perpendicular to the grown direction of the
well. We find that it is possible to confine excitons into one-dimensional (1D)
traps. We show that the dependence of the confinement energy on the exciton
wave vector, which is related to its free direction of motion along the wire
direction, is very small. Through the application of a background magnetic
field it is possible to move the position of the trapping region towards the
edge of the ferromagnetic stripe or even underneath the stripe. The exact
position of this 1D exciton channel depends on the strength of the background
magnetic field and on the magnetic polarisation direction of the ferromagnetic
film.Comment: 10 pages, 7 figures, to be published in J. Phys: Condens. Matte
Experimental demonstration of a mu=-1 metamaterial lens for magnetic resonance imaging
In this work a mu=-1 metamaterial (MM) lens for magnetic resonance imaging
(MRI) is demonstrated. MRI uses surface coils to detect the radiofrequency(RF)
energy absorbed and emitted by the nuclear spins in the imaged object. The
proposed MM lens manipulates the RF field detected by these surface coils, so
that the coil sensitivity and spatial localization is substantially improved.
Beyond this specific application, we feel that the reported results are the
experimental confirmation of a new concept for the manipulation of RF field in
MRI, which paves the way to many other interesting applications.Comment: 9 pages, 3 figure
Domain wall description of superconductivity
In the present work we shall address the issue of electrical conductivity in
superconductors in the perspective of superconducting domain wall solutions in
the realm of field theory. We take our set up made out of a dynamical complex
scalar field coupled to gauge field to be responsible for superconductivity and
an extra scalar real field that plays the role of superconducting domain walls.
The temperature of the system is interpreted through the fact that the soliton
following accelerating orbits is a Rindler observer experiencing a thermal
bath.Comment: 9 pages, 5 figures, Latex. Version to appear in PL
Constraining the relative inclinations of the planets B and C of the millisecond pulsar PSR B1257+12
We investigate on the relative inclination of the planets B and C orbiting
the pulsar PSR B1257+12 in connection with potential violations of the
equivalence principle (Abridged).Comment: LaTex2e, 10 pages, 1 table, 3 figures, 17 references. Small stylistic
changes. Version to appear in Journal of Astrophysics and Astronomy (JAA
The role of organizational climate, and work–family conflict in burnout: The case of teachers
Burnout is a major concern for the scientific and educational community, as it leads to harmful consequences, both at a personal and organizational level. Several studies showed that burnout is influenced by multiple factors, including organizational climate and work–family conflict. However, studies analyzing these three variables together in the educational sector are scarce. Thus, this study aimed to analyze whether the organizational climate influenced burnout through work–family conflict. We collected data in two-time points with 253 teachers. The results showed that only the organizational climate dimensions of involvement, control, autonomy, task orientation, and physical comfort were associated with burnout. Plus, only the physical comfort and autonomy climates significantly reduced burnout via the decreases in work–family conflict. Thus, these organizational climates’ dimensions seem to be essential factors to reduce not only work–family conflict but also burnout in the educational sector. This study tested the mediating role of work–family conflict on the link between organizational climate and burnout, with a group of teachers. Additionally, the data was collected during the pandemic crisis of COVID-19.info:eu-repo/semantics/publishedVersio
Pulsar J1411+2551: A Low Mass New Double Neutron Star System
In this work, we report the discovery and characterization of PSR J1411+2551,
a new binary pulsar discovered in the Arecibo 327 MHz Drift Pulsar Survey. Our
timing observations of the radio pulsar in the system span a period of about
2.5 years. This timing campaign allowed a precise measurement of its spin
period (62.4 ms) and its derivative (9.6 0.7) ; from these, we derive a characteristic age of Gyr and a
surface magnetic field strength of 2.5 G. These numbers
indicate that this pulsar was mildly recycled by accretion of matter from the
progenitor of the companion star. The system has an eccentric ()
2.61 day orbit. This eccentricity allows a highly significant measurement of
the rate of advance of periastron, . Assuming general relativity accurately models the
orbital motion, this implies a total system mass M = . The minimum companion mass is and the maximum
pulsar mass is . The large companion mass and the orbital
eccentricity suggest that PSR J1411+2551 is a double neutron star system; the
lightest known to date including the DNS merger GW 170817. Furthermore, the
relatively low orbital eccentricity and small proper motion limits suggest that
the second supernova had a relatively small associated kick; this and the low
system mass suggest that it was an ultra-stripped supernova.Comment: Accepted for publication in APJ letter
Pulsar J0453+1559: A Double Neutron Star System with a Large Mass Asymmetry
To understand the nature of supernovae and neutron star (NS) formation, as
well as binary stellar evolution and their interactions, it is important to
probe the distribution of NS masses. Until now, all double NS (DNS) systems
have been measured to have a mass ratio close to unity (q 0.91). Here we
report the measurement of the individual masses of the 4.07-day binary pulsar
J0453+1559 from measurements of the rate of advance of periastron and Shapiro
delay: The mass of the pulsar is 1.559(5) and that of its companion
is 1.174(4) ; q = 0.75. If this companion is also a neutron star
(NS), as indicated by the orbital eccentricity of the system (e=0.11), then its
mass is the smallest precisely measured for any such object. The pulsar has a
spin period of 45.7 ms and a spin derivative of 1.8616(7) x; from these
we derive a characteristic age of ~ 4.1 x years and a magnetic field of
~ 2.9 x G,i.e, this pulsar was mildly recycled by accretion of matter
from the progenitor of the companion star. This suggests that it was formed
with (very approximately) its current mass. Thus NSs form with a wide range of
masses, which is important for understanding their formation in supernovae. It
is also important for the search for gravitational waves released during a
NS-NS merger: it is now evident that we should not assume all DNS systems are
symmetric
Manual de perdas pós-colheita em frutos e hortaliças.
Produção e perdas de frutos e hortaliças no Brasil. Perdas: definição, tipos e causas. Alguns aspectos envolvidos no controle das perdas: pré-colheita; colheita; pós-colheita; embalagem; transporte; armazenamento. Aspectos de mercado.bitstream/item/33932/1/1997-DOC-0027.pd
- …