8,675 research outputs found
Quantum phases of a qutrit
We consider various approaches to treat the phases of a qutrit. Although it
is possible to represent qutrits in a convenient geometrical manner by
resorting to a generalization of the Poincare sphere, we argue that the
appropriate way of dealing with this problem is through phase operators
associated with the algebra su(3). The rather unusual properties of these
phases are caused by the small dimension of the system and are explored in
detail. We also examine the positive operator-valued measures that can describe
the qutrit phase properties.Comment: 6 page
Porous medium equation with nonlocal pressure
We provide a rather complete description of the results obtained so far on
the nonlinear diffusion equation , which describes a flow through a porous medium driven by a
nonlocal pressure. We consider constant parameters and , we assume
that the solutions are non-negative, and the problem is posed in the whole
space. We present a theory of existence of solutions, results on uniqueness,
and relation to other models. As new results of this paper, we prove the
existence of self-similar solutions in the range when and , and the
asymptotic behavior of solutions when . The cases and were
rather well known.Comment: 24 pages, 2 figure
Active Galactic Nuclei with Candidate Intermediate-Mass Black Holes
We present an initial sample of 19 intermediate-mass black hole candidates in
active galactic nuclei culled from the First Data Release of the Sloan Digital
Sky Survey. Using the linewidth-luminosity-mass scaling relation established
for broad-line active nuclei, we estimate black hole masses in the range of 8 x
10^4 - 10^6 solar masses, a regime in which only two objects are currently
known. The absolute magnitudes are faint for active galactic nuclei, ranging
from M_g of -15 to -18 mag, while the bolometric luminosities are all close to
the Eddington limit. The entire sample formally satisfies the linewidth
criterion for so-called narrow-line Seyfert 1 galaxies; however, they display a
wider range of FeII and [OIII] (5007) line strengths than is typically observed
in this class of objects. Although the available imaging data are of
insufficient quality to ascertain the detailed morphologies of the host
galaxies, it is likely that the majority of the hosts are relatively late-type
systems. The host galaxies have estimated g-band luminosities ~ 1 mag fainter
than M* for the general galaxy population at z of 0.1. Beyond simply extending
the known mass range of central black holes in galactic nuclei, these objects
provide unique observational constraints on the progenitors of supermassive
black holes. They are also expected to contribute significantly to the
integrated signal for future gravitational wave experiments.Comment: ApJ Accepted, 13 pages, 9 figures, uses emulateapj.cl
Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor
We report the controlled integration, via Dip Pen Nanolithography, of
monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the
most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling
between these nanomagnets and the microSQUID improves the achievable
sensitivity by a factor 100, enabling us to measure the linear susceptibility
of the molecular array down to very low temperatures (13 mK). This method opens
the possibility of applying ac susceptibility experiments to characterize
two-dimensional arrays of single molecule magnets within a wide range of
temperatures and frequencies.Comment: 4 pages 3 figure
Muon spin rotation and neutron scattering study of the non-centrosymmetric tetragonal compound CeAuAl3
We have investigated the non-centrosymmetric tetragonal heavy-fermion
compound CeAuAl3 using muon spin rotation (muSR), neutron diffraction (ND) and
inelastic neutron scattering (INS) measurements. We have also revisited the
magnetic, transport and thermal properties. The magnetic susceptibility reveals
an antiferromagnetic transition at 1.1 K with a possibility of another magnetic
transition near 0.18 K. The heat capacity shows a sharp lambda-type anomaly at
1.1 K in zero-filed, which broadens and moves to higher temperature in applied
magnetic field. Our zero-field muSR and ND measurements confirm the existence
of a long-range magnetic ground state below 1.2 K. Further the ND study reveals
an incommensurate magnetic ordering with a magnetic propagation vector k = (0,
0, 0.52) and a spiral structure of Ce moments coupled ferromagnetically within
the ab-plane. Our INS study reveals the presence of two well-defined crystal
electric field (CEF) excitations at 5.1 meV and 24.6 meV in the paramagnetic
phase of CeAuAl3 which can be explained on the basis of the CEF theory.
Furthermore, low energy quasi-elastic excitations show a Gaussian line shape
below 30 K compared to a Lorentzian line shape above 30 K, indicating a
slowdown of spin fluctuation below 30 K. We have estimated a Kondo temperature
of TK=3.5 K from the quasi-elastic linewidth, which is in good agreement with
that estimated from the heat capacity. This study also indicates the absence of
any CEF-phonon coupling unlike that observed in isostructural CeCuAl3. The CEF
parameters, energy level scheme and their wave functions obtained from the
analysis of INS data explain satisfactorily the single crystal susceptibility
in the presence of two-ion anisotropic exchange interaction in CeAuAl3.Comment: 28 pages and 17 figure
Statistical Properties of Radio Emission from the Palomar Seyfert Galaxies
We have carried out an analysis of the radio and optical properties of a
statistical sample of 45 Seyfert galaxies from the Palomar spectroscopic survey
of nearby galaxies. We find that the space density of bright galaxies (-22 mag
<= M_{B_T} <= -18 mag) showing Seyfert activity is (1.25 +/- 0.38) X 10^{-3}
Mpc^{-3}, considerably higher than found in other Seyfert samples. Host galaxy
types, radio spectra, and radio source sizes are uncorrelated with Seyfert
type, as predicted by the unified schemes for active galaxies. Approximately
half of the detected galaxies have flat or inverted radio spectra, more than
expected based on previous samples. Surprisingly, Seyfert 1 galaxies are found
to have somewhat stronger radio sources than Seyfert 2 galaxies at 6 and 20 cm,
particularly among the galaxies with the weakest nuclear activity. We suggest
that this difference can be accommodated in the unified schemes if a minimum
level of Seyfert activity is required for a radio source to emerge from the
vicinity of the active nucleus. Below this level, Seyfert radio sources might
be suppressed by free-free absorption associated with the nuclear torus or a
compact narrow-line region, thus accounting for both the weakness of the radio
emission and the preponderance of flat spectra. Alternatively, the flat spectra
and weak radio sources might indicate that the weak active nuclei are fed by
advection-dominated accretion disks.Comment: 18 pages using emulateapj5, 13 embedded figures, accepted by Ap
Discovery of Radio Outbursts in the Active Nucleus of M81
The low-luminosity active galactic nucleus of M81 has been monitored at
centimeter wavelengths since early 1993 as a by-product of radio programs to
study the radio emission from Supernova 1993J. The extensive data sets reveal
that the nucleus experienced several radio outbursts during the monitoring
period. At 2 and 3.6 cm, the main outburst occurred roughly in the beginning of
1993 September and lasted for approximately three months; at longer
wavelengths, the maximum flux density decreases, and the onset of the burst is
delayed. These characteristics qualitatively resemble the standard model for
adiabatically expanding radio sources, although certain discrepancies between
the observations and the theoretical predictions suggest that the model is too
simplistic. In addition to the large-amplitude, prolonged variations, we also
detected milder changes in the flux density at 3.6 cm and possibly at 6 cm on
short (less than 1 day) timescales. We discuss a possible association between
the radio activity and an optical flare observed during the period that the
nucleus was monitored at radio wavelengths.Comment: To appear in The Astronomical Journal. Latex, 18 pages including
embedded figures and table
Fórmulas de inmunonutrición enteral en la cirugía del cáncer de cabeza y cuello: Una revisión sitemática
Introduction: Significant malnutrition exists in a high
percentage of patients with head and neck cancer. Malnutrition
is associated with defects in immune function that
may impair the host response to malignancy. Malnutrition
and immunosupression make patients highly susceptible
to postoperative infections and complications.
Objectives: Some studies of patients receiving immunonutrition
in the perioperative period in head and neck
cancer have shown beneficial effects on clinical outcome
and inmune status. The authors carried out a systematic
review of randomised control trials to determine whether
perioperative immunonutrition has a role in the treatment
of head and neck cancer.
Methods: 14 trials of polymeric nutritional supplementation
with immunonutrition were identified. Two studies
compared two types of immunonutrition.
Results: A reduction in the length of postoperative
hospital stay was seen in some trials, but the reason for
this reduction is not clear. Some studides showed statistical
differences with less complications in arginineenhanced
group and also showed a significant decrease of
fistula complications in patients treated with a high arginine
dose enhanced formula, if compared with a medium
dose of arginine.
Conclussion: Those planning future studies face
challenges. A suitable powered clinical trial is required
before firm recommendations can be made on the use of
immunonutrition in head and neck cancer patients postoperativelyIntroducción: Un alto porcentaje de pacientes con cáncer
de cabeza y cuello presentan un importante grado de
malnutrición. Esta malnutrición está asociada defectos de
la función inmune. Tanto la malnutrición como la inmunosupresión
hacen a estos pacientes susceptibles de padecer
complicaciones infecciosas en el postoperatorio.
Objetivos: Algunos trabajos de pacientes que han recibido
inmunonutrición en el postoperatorio de cirugía por
cáncer de cabeza y cuello han mostrado un efecto beneficioso
en la evolución clínica y el estado inmune. Los autores
han llevado a cabo una revisión sistemática de los
ensayos clínicos realizados hasta la fecha, para determinar
el papel que tiene la inmunonutrición enteral postoperatoria
en el tratamiento del cáncer de cabeza y cuello.
Métodos: Se identificaron 14 trabajos en los que se
habían utilizado fórmulas de inmunonutrición. Dos trabajos
compararon dos tipos de inmunonutrición. Resultados:
En algunos trabajos se observó una disminución en
los días de estancia hospitalaria, aunque la razón para
ello no está clara. Algunos estudios mostraron diferencias
significativas con menos complicaciones en los grupos que
recibieron nutriciones enriquecidas, presentando una
disminución significativa en el número de fístulas en
pacientes tratados con nutriciones con altas dosis de arginina,
si se compara con una nutrición con una dosis media
de arginina.
Conclusión: Los futuros trabajos presentan retos. Es
necesario un ensayo clínico extenso, para poder realizar
recomendaciones firmes sobre el uso de la inmunonutrición
en el postoperatorio de pacientes intervenidos de
cáncer de cabeza y cuell
Epifisiólisis femoral proxima: revisión de 44 casos
Se revisan 44 niños con 47 epifisiólisis femorales proximales. Veintitrés desplazamientos
fueron leves, 18 moderados y 6 severos. Todas las epifisiólisis excepto 1 se trataron quirúrgicamente.
En 10 casos se fijó profilácticamente la cadera contralateral. Existió penetración
articular por el implante en 17 (30%) de las 56 caderas fijadas. El seguimiento medio ha sido de
56 meses (rango: 3 a 148 meses). Los resultados, según criterios clínicos y radiográficos, han sido
excelentes o buenos en el 91% de los deslizamientos leves, el 77% de los moderados y el 33% de
los severos. Las complicaciones fueron 2 casos de condrólisis, ambos asociados a penetración articular.
En 2 (6%) de los pacientes donde no se realización profiláctica se produjo deslizamiento
contralateral. En nuestro estudio los resultados se correlacionan con la cuantía del deslizamiento.
No recomendamos la fijación profiláctica contraletal.We review 44 children with 47 slipped capital femoral epiphysis. There were
23 mild slips, 18 moderate, and 6 severe. Operative treatment was performed in all but one of the
slips. In 10 cases prophylactic pinning of the contralateral hip was performed. Penetration of the
joint by the implant was present in 17 (30%) of the 56 fixed hips. The average follow-up was 56
months (range: 3 to 178 months). The results, according to clinical and rocntgenographic parameters
were excellent or good in 91% of mild slips, 77% of moderate and 33% of severe. As complications
there were two cases of chondrolysis, both associated with joint penetration. In 2 (6%) patients
where prophylactic pinning was not performed, contralateral hip slipping developed. In our study,
results correlate with slip severity. We do not recommend prophylactic contralateral pinning
Design of the Front End Electronics for the Infrared Camera of JEM-EUSO, and manufacturing and verification of the prototype model
The Japanese Experiment Module (JEM) Extreme Universe Space Observatory
(EUSO) will be launched and attached to the Japanese module of the
International Space Station (ISS). Its aim is to observe UV photon tracks
produced by ultra-high energy cosmic rays developing in the atmosphere and
producing extensive air showers.
The key element of the instrument is a very wide-field, very fast,
large-lense telescope that can detect extreme energy particles with energy
above eV. The Atmospheric Monitoring System (AMS), comprising, among
others, the Infrared Camera (IRCAM), which is the Spanish contribution, plays a
fundamental role in the understanding of the atmospheric conditions in the
Field of View (FoV) of the telescope. It is used to detect the temperature of
clouds and to obtain the cloud coverage and cloud top altitude during the
observation period of the JEM-EUSO main instrument. SENER is responsible for
the preliminary design of the Front End Electronics (FEE) of the Infrared
Camera, based on an uncooled microbolometer, and the manufacturing and
verification of the prototype model. This paper describes the flight design
drivers and key factors to achieve the target features, namely, detector
biasing with electrical noise better than V from Hz to MHz,
temperature control of the microbolometer, from C to C
with stability better than mK over hours, low noise high bandwidth
amplifier adaptation of the microbolometer output to differential input before
analog to digital conversion, housekeeping generation, microbolometer control,
and image accumulation for noise reduction
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