219 research outputs found
Parametric Oscillation with Squeezed Vacuum Reservoirs
Employing the quantum Hamiltonian describing the interaction of two-mode
light (signal-idler modes) generated by a nondegenerate parametric oscillator
(NDPO) with two uncorrelated squeezed vacuum reservoirs (USVR), we derive the
master equation. The corresponding Fokker-Planck equation for the Q-function is
then solved employing a propagator method developed in Ref. \cite{1}. Making
use of this Q-function, we calculate the quadrature fluctuations of the optical
system. From these results we infer that the signal-idler modes are in squeezed
states and the squeezing occurs in the first quadrature. When the NDPO operates
below threshold we show that, for a large squeezing parameter, a squeezing
amounting to a noise suppression approaching 100% below the vacuum level in the
first quadrature can be achieved.Comment: 16 page
Quantum Fluctuations of Low Dimensional Bose-Einstein Condensates in Optical Systems
A system of low dimensional condensed ultracold atomic gases inside a field of a laser-driven optical cavity exhibits dispersive optical bistability. During such a process the system also
shows quantum fluctuations. Condensate fluctuations are highly manifested particularly in low dimensional systems. In this paper we have investigated the theory and manifestation of
fluctuations in quantum optical systems in low dimensional Bose-Einstein condensates. We have described the system using the mean-field approximation. In this study we have verified that low dimensional quantum gases exhibit not only highly fascinating properties but also we have indicated that the use of mean field theory to describe quantum gases in low dimensions is highly restricted since the possibility of generating low dimensional bosonic condensates is dominated by the existence of highly sensitive and intrinsic quantum fluctuations
Splitting and merging an elongated Bose-Einstein condensate at finite temperature
We analyze coherence effects during the splitting of a quasi one-dimensional
condensate into two spatially separated ones and their subsequent merging into
a single condensate. Our analysis takes into account finite-temperature
effects, where phase fluctuations play an important role. We show that, at
zero-temperature, the two split condensates can be merged into a single one
with a negligible phase difference. By increasing temperature to a finite value
below the critical point for condensation (), i.e., , a
considerable enhancement of phase and density fluctuations appears during the
process of splitting and merging. Our results show that if the process of
splitting and merging is sufficiently adiabatic, the whole process is quite
insensitive to phase fluctuations and even at high temperatures, a single
condensate can be produced.Comment: 8 pages, 6 figure
Bottlenecks in the provision of quality mental health services in Eritrea
Background: The prevalence of mental disorders is increasing significantly in developing countries due to the frequently occurring major risk factors. There is no published information on the profile of mental health disorder and services in Eritrea.
Objective of the study: Follow-up descriptive study was conducted on one hundred and one consecutive children with advanced HIV disease who were put on antiretroviral therapy from September 2005 to October 2006. These patients were followed up at the antiretroviral therapy (ART) clinic of the hospital.
Methods: A descriptive cross sectional study was conducted using the WHO-AIMS questionnaire that was administered to relevant stakeholders.
Results: There was no comprehensive mental health policy and legislation in Eritrea. Only 5% of the health services budget is allocated for mental health services. Mental health services is free of charge and were provided integrated with Primary Health Care services. Inadequate human resources and inadequate training on mental health for the health workers were among the constraints.
Conclusion: The status of mental disorders and the mental health services in Eritrea from the policy to management guidelines requires urgent review.
Significant Outcomes: a) In resource limited settings, the integrated primary health care approach for mental health services is cost effective and avoids associated stigma.
b) WHO/AIMS tool is a simple tool that provides complete picture of the mental health system of a country,
c) Lack of policies and legislation in a country severely affects the mental health system of a country
Limitations: This was a cross sectional study where data collection and analysis was partially restricted by the level and quality of information available in the registry books of the health facilities.
Key words: WHO-AIMS, integrated primary health care, mental health services
Two-Stage Kondo Effect and Kondo Box Level Spectroscopy in a Carbon Nanotube
The concept of the "Kondo box" describes a single spin, antiferromagnetically
coupled to a quantum dot with a finite level spacing. Here, a Kondo box is
formed in a carbon nanotube interacting with a localized electron. We
investigate the spins of its first few eigenstates and compare them to a recent
theory. In an 'open' Kondo-box, strongly coupled to the leads, we observe a
non-monotonic temperature dependence of the nanotube conductance, which results
from a competition between the Kondo-box singlet and the 'conventional' Kondo
state that couples the nanotube to the leads.Comment: 5 pages, 3 figure
Resonant Tunneling in a Dissipative Environment
We measure tunneling through a single quantum level in a carbon nanotube
quantum dot connected to resistive metal leads. For the electrons tunneling
to/from the nanotube, the leads serve as a dissipative environment, which
suppresses the tunneling rate. In the regime of sequential tunneling, the
height of the single-electron conductance peaks increases as the temperature is
lowered, although it scales more weekly than the conventional 1/T. In the
resonant tunneling regime (temperature smaller than the level width), the peak
width approaches saturation, while the peak height starts to decrease. Overall,
the peak height shows a non-monotonic temperature dependence. We associate this
unusual behavior with the transition from the sequential to the resonant
tunneling through a single quantum level in a dissipative environment.Comment: 5 pages, 5 figure
Quantum switches and quantum memories for matter-wave lattice solitons
We study the possibility of implementing a quantum switch and a quantum
memory for matter wave lattice solitons by making them interact with
"effective" potentials (barrier/well) corresponding to defects of the optical
lattice. In the case of interaction with an "effective" potential barrier, the
bright lattice soliton experiences an abrupt transition from complete
transmission to complete reflection (quantum switch) for a critical height of
the barrier. The trapping of the soliton in an "effective" potential well and
its release on demand, without loses, shows the feasibility of using the system
as a quantum memory. The inclusion of defects as a way of controlling the
interactions between two solitons is also reported
The longitudinal variability of equatorial electrojet and vertical drift velocity in the African and American sectors
While the formation of equatorial electrojet (EEJ) and its temporal
variation is believed to be fairly well understood, the longitudinal
variability at all local times is still unknown. This paper presents a case
and statistical study of the longitudinal variability of dayside EEJ for all
local times using ground-based observations. We found EEJ is stronger in the
west American sector and decreases from west to east longitudinal sectors.
We also confirm the presence of significant longitudinal difference in the
dusk sector pre-reversal drift, using the ion velocity meter (IVM)
instrument onboard the C/NOFS satellite, with stronger pre-reversal drift in
the west American sector compared to the African sector. Previous satellite
observations have shown that the African sector is home to stronger and
year-round ionospheric bubbles/irregularities compared to the American and
Asian sectors. This study's results raises the question if the vertical
drift, which is believed to be the main cause for the enhancement of
Rayleigh–Taylor (RT) instability growth rate, is stronger in the American
sector and weaker in the African sector – why are the occurrence and
amplitude of equatorial irregularities stronger in the African sector
Analysis of maternal and newborn training curricula and approaches to inform future trainings for routine care, basic and comprehensive emergency obstetric and newborn care in the low- and middle-income countries: Lessons from Ethiopia and Nepal
Program managers routinely design and implement specialised maternal and newborn health trainings for health workers in low- and middle-income countries to provide better-coordinated care across the continuum of care. However, in these countries details on the availability of different training packages, skills covered in those training packages and the gaps in their implementation are patchy. This paper presents an assessment of maternal and newborn health training packages to describe differences in training contents and implementation approaches used for a range of training packages in Ethiopia and Nepal. We conducted a mixed-methods study. The quantitative assessment was conducted using a comprehensive assessment questionnaire based on validated WHO guidelines and developed jointly with global maternal and newborn health experts. The qualitative assessment was conducted through key informant interviews with national stakeholders involved in implementing these training packages and working with the Ministries of Health in both countries. Our quantitative analysis revealed several key gaps in the technical content of maternal and newborn health training packages in both countries. Our qualitative results from key informant interviews provided additional insights by highlighting several issues with trainings related to quality, skill retention, logistics, and management. Taken together, our findings suggest four key areas of improvement: first, training materials should be updated based on the content gaps identified and should be aligned with each other. Second, trainings should address actual health worker performance gaps using a variety of innovative approaches such as blended and self-directed learning. Third, post-training supervision and ongoing mentoring need to be strengthened. Lastly, functional training information systems are required to support planning efforts in both countries
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