15,563 research outputs found
A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses
Multipath propagation in the interstellar medium distorts radio pulses, an
effect predominant for distant pulsars observed at low frequencies. Typically,
broadened pulses are analyzed to determine the amount of propagation-induced
pulse broadening, but with little interest in determining the undistorted pulse
shapes. In this paper we develop and apply a method that recovers both the
intrinsic pulse shape and the pulse broadening function that describes the
scattering of an impulse. The method resembles the CLEAN algorithm used in
synthesis imaging applications, although we search for the best pulse
broadening function, and perform a true deconvolution to recover intrinsic
pulse structre. As figures of merit to optimize the deconvolution, we use the
positivity and symmetry of the deconvolved result along with the mean square
residual and the number of points below a given threshold. Our method makes no
prior assumptions about the intrinsic pulse shape and can be used for a range
of scattering functions for the interstellar medium. It can therefore be
applied to a wider variety of measured pulse shapes and degrees of scattering
than the previous approaches. We apply the technique to both simulated data and
data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Bose-Einstein Condensates in Rotating Lattices
Strongly interacting bosons in 2D in a rotating square lattice are
investigated via a modified Bose-Hubbard Hamiltonian. Such a system corresponds
to a rotating lattice potential imprinted on a trapped Bose-Einstein
condensate. Second-order quantum phase transitions between states of different
symmetries are observed at discrete rotation rates. For the square lattice we
study, there are four possible ground-state symmetries.Comment: 4 pages, 5 figures, Accepted for publication in PRL v2: Replaced
phase winding labels with symmetry eigenstate indices, replaced Gaussian
Ansatz with more general treatment and other minor change
Non-resonant microwave absorption studies of superconducting MgB_2
Non-resonant microwave absorption(NRMA) studies of superconducting MgB_2 at a
frequency of 9.43 GHz in the field range -50 Gauss to 5000 Gauss are reported.
The NRMA results indicate near absence of intergranular weak links. A linear
temperature dependence of the lower critical field H_c1 is observed indicating
a non s-wave superconductivity. However, the phase reversal of the NRMA signal
which could suggest d-wave symmetry is also not observed.Comment: 8 pages, 2 figure
Wireless Sensor Networks: A Performance Study of IEEE 802.15.4 Standard
Wireless Sensor Networks (WSN) play a key role in sensing, computing and communicating the information in most of the fields bringing substantial improvements in a broad spectrum of modern technologies. Data to be routed from source to destination is very difficult in WSN due to
the mobility of the network elements and lack of central administration. In this paper an attempt has been made to evaluate the performance of routing protocol Ad-hoc On-demand Distance Vector routing (AODV) for the wireless sensor nodes(IEEE 802.15.4 standard). The performance of
routing protocol is analysed using various metrics like total packets received, throughput, average end-to-end delay, total bytes received and average jitter using Qualnet 5.0.2 simulator
Acute ST-segment elevation myocardial infarction in a young patient with essential thrombocythemia: a case with long-term follow-up report
Essential thrombocythemia (ET) is a neoplastic proliferation of mature myeloid cells - in particular, megakaryocytes - leading to persistently elevated platelet count. Usual clinical presentation is related to an increase in the risk of hemorrhage and/or thrombosis. Management of ET consists of antiplatelet therapies - mainly aspirin and cytoreductive therapies. Coronary involvement in patients with ET is rare. The optimal treatment strategies for ET patients presenting with acute myocardial infarction remains unclear. Acute interventions like intracoronary thrombolytic therapy, angioplasty, and coronary-artery bypass grafting have been reported in such patients. However, several questions remain unanswered about the acute and long-term management of these patients. Herein, we report the case of a 47-year-old female who presented with acute myocardial infarction as the first clinical sign of ET, and also present the long-term follow-up of this patient
A Performance Study of Proactive, Reactive and Hybrid Routing Protocols using Qualnet Simulator
The advancement in information technology and the need for
large-scale communication infrastructures has triggered the era of Wireless Sensor Networks (WSNs). Mobile ad-hoc network (MANET) is a network of wireless mobile nodes which
communicate with each other without any centralized
control or established infrastructure. Routing is the process of selecting paths in a network along which data is to be sent. Routing is a critical task in MANET where the nodes are mobile. Dynamic and reliable routing protocols are required in the ad-hoc wireless networks, as they have no infrastructure (base station) and their network topology changes. There are various protocols for handling the routing problem in the ad-hoc wireless network environment. In this paper focus is given on studying the performance evaluation of various routing protocols using Qualnet simulator 5.0.2. The performance of the proactive, reactive and hybrid protocols are analyzed with different node densities for mobile and stationary nodes. The metrics used for the performance evaluation include average jitter, throughput, packet delivery ratio and average end to end
delay
1.57 μm InGaAsP/InP surface emitting lasers by angled focus ion beam etching
The characteristics of 1.57 μm InGaAsP/InP surface emitting lasers based on an in-plan ridged structure and 45° beam deflectors defined by angled focused ion beam (FIB) etching are reported. With an externally integrated beam deflector, threshold currents and emission spectra identical to conventional edge emitting lasers are achieved. These results show that FIB etching is a very promising technique for the definition of high quality mirrors and beam deflectors on semiconductor heterostructures for a variety of integrated optoelectronic devices
Scenario Based Study of On-demand reactive routing protocol for IEEE-802.11 and 802.15.4 standards
Routing data from source to destination is hard in
Mobile Ad-Hoc Networks (MANET) due to the mobility of the network elements and lack of central administration. The main method for evaluating the performance of MANETs is simulation. In this paper performance of Ad-hoc On-demand Distance Vector (AODV) reactive routing protocol is studied by considering IEEE 802.11 and IEEE 802.15.4 standards. Metrics like average end-to-end delay, packet delivery ratio, total bytes received and throughput are considered for investigating simulation scenario by varying network size with 10 mps node mobility. Also simulation has been carried out by varying mobility for scenario with 50 nodes
- …