57 research outputs found
Observations of TeV gamma-rays from Mrk 421 during Dec. 2005 to Apr. 2006 with the TACTIC telescope
The TACTIC -ray telescope has observed Mrk 421 on 66 clear nights
from Dec. 07, 2005 to Apr. 30, 2006, totalling 202 hours of on-source
observations. Here, we report the detection of flaring activity from the source
at 1 TeV energy and the time-averaged differential -ray spectrum
in the energy range 1-11 TeV for the data taken between Dec. 27, 2005 to Feb.
07, 2006 when the source was in a relatively higher state as compared to the
rest of the observation period. Analysis of this data spell, comprising about
97h reveals the presence of a -ray signal with
daily flux of 1 Crab unit on several days. A pure power law spectrum with
exponent as well as a power law spectrum with an exponential
cutoff and are found to provide
reasonable fits to the inferred differential spectrum within statistical
uncertainties. We believe that the TeV light curve presented here, for nearly 5
months of extensive coverage, as well as the spectral information at
-ray energies of 5 TeV provide a useful input for other groups
working in the field of -ray astronomy.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic
New Physics Contribution to Neutral Trilinear Gauge Boson Couplings
We study the one loop new physics effects to the CP even triple neutral gauge
boson vertices , ,
and in the context of Little Higgs models. We compute the
contribution of the additional fermions in Littles Higgs model in the framework
of direct product groups where gauge symmetry is
embedded in SU(5) global symmetry and also in the framework of simple group
where gauge symmetry breaks down to . We
calculate the contribution of the fermions to these couplings when parity
is invoked. In addition, we re-examine the MSSM contribution at the chosen
point of SPS1a' and compare with the SM and Little Higgs models.Comment: 19 pages, 5 figures, 3 table
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
Seller’s optimal credit period and replenishment time in a supply chain with up-stream and down-stream trade credits
[[abstract]]In practice, a supplier often offers its retailers a permissible delay period M to settle their unpaid accounts. Likewise, a retailer in turn offers another trade credit period N to its customers. The benefits of trade credit are not only to attract new buyers who consider it a type of price reduction, but also to provide a competitive strategy other than introduce permanent price reductions. On the other hand, the policy of granting credit terms adds an additional cost to the seller as well as an additional dimension of default risk. In this paper, we first incorporate the fact that trade credit has a positive impact on demand but negative impacts on costs and default risks to establish an economic order quantity model for the seller in a supply chain with up-stream and down-stream trade credits. Then we derive the necessary and sufficient conditions to obtain the optimal replenishment time and credit period for the seller. Finally, we use some numerical examples to illustrate the theoretical results.[[incitationindex]]SCI[[booktype]]電子
Treatment of baseflow from an urban catchment by a floating wetland system
This study investigated the performance of a floating wetlands system (FWS) planted with Chrysopogon
zizanioides (Vetiver grass), Typha angustifolia and Polygonum barbatum as treatment units to remove nutrients
contained in the baseflow to the Kranji reservoir in Singapore. Phase 1 of the study consisted of
controlled experiments with a perspex floating wetland test cell of dimensions 2.5 m
×2 m
×1 m. Separate
experiments were carried out using the inflows from Sungei Kangkar, Sungei Tengah and Sungei
Peng Siang, which drain into Kranji reservoir. Tests were conducted for each plant species using water
taken from each of the tributaries in turn. Water samples were collected from the experimental and
control tanks during the experiment and analysed for total nitrogen, TN (mg/L), total phosphorus, TP
(mg/L), orthophosphate, OP (mg/L) as PO4 and ammoniacal nitrogen, AN (mg/L) as NH4+. The net nutrient
reduction (%) for Vetiver, Typha and Polygonum were 19.1, 39.2 and 46.0 for TP, and 40.8, 67.5, 7.8 for TN,
respectively. The rate of decrease of nutrients was found to be significant within the first few days and
reached steady state after approximately 10 days. The removal coefficient (day−1) for Vetiver, Typha and
Polygonum were 0.66, 0.87 and 1.06 for TP and 0.64, 0.68, 0.87 for TN, respectively. The removals of OP and
AN could not be ascertained due to the low concentrations of these parameters contained in the waters
tested. In Phase 2, field experiments were carried out with the FWS installed in Sungei Peng Siang with
the same plant species that were used in the controlled experiments. The growth of Vetiver and Typha was
monitored while all three plant species were tested for plant nutrient content. Plant TN and TP content
increased rapidly during the initial rapid growth stage, reached a maximum after approximately 1 month
and decreased. Typha achieved the highest rate of increase in nutrient content compared to Vetiver and
Polygonum. The uptake of TN by Typha, Vetiver and Polygonum was estimated to be 16.2, 1.74 and 2.82
(mg/day m2). The corresponding uptake for TP was 1.57, 0.16 and 0.4 (mg/day m2). For Typha, the mat
size required for 50% removal of TN and TP from the baseflow was estimated to be 0.056 and 0.031 ha of
mat/ha of catchment area. This is a conservative estimate since nutrient uptake by the root system was
ignored
Predicting time-dependent pier scour depth with support vector regression
The temporal variation of local pier scour depth is very complex, especially for cases where the bed comprises a sediment mixture. Many semi-empirical models have been proposed to predict the time-dependent local pier scour depth. In this paper, an alternative approach, the support vector regression method (SVR) is used to estimate the temporal variation of pier-scour depth with non-uniform sediments under clear-water conditions. Based on dimensional analyses, the temporal variation of scour depth was modeled as a function of seven dimensionless input parameters, namely flow shallowness (y/Dp), sediment coarseness (Dp/d50), densimetric Froude number (Fd), the difference between the actual and critical densimetric Froude number (Fd − Fdβ), geometric standard deviation of the sediment particle size distribution (σg), pier Froude number (U/gDp) and one of the following three dimensionless time scales (T1 = t/tR1, T2 = t/tR2 and T3 = t/tR3). The SVR model not only estimates the time-dependent scour depth more accurately than conventional regression models, but also provides results that are consistent with the physics of the scouring process
Preparation and Characterisation of Heteronuclear Mixed Ligand Complexes of Aluminium Containing Organosilicon/Organotin Moieties
Evaluating the Diagnostic Performance of Prehospital Stroke Scales Across the Range of Deficit Severity: Analysis of the Prehospital Triage of Patients With Suspected Stroke Study
BACKGROUND: The usefulness of prehospital scales for identifying anterior circulation large vessel occlusion (aLVO) in patients with suspected stroke may vary depending on the severity of their presentation. The performance of these scales across the spectrum of deficit severity is unclear. The aim of this study was to evaluate the diagnostic performance of 8 prehospital scales for identifying aLVO across the spectrum of deficit severity. METHODS: We used data from the PRESTO study (Prehospital Triage of Patients With Suspected Stroke Symptoms), a prospective observational study comparing prehospital stroke scales in detecting aLVO in suspected stroke patients. We used the National Institutes of Health Stroke Scale (NIHSS) score, assessed in-hospital, as a proxy for the Clinical Global Impression of stroke severity during prehospital assessment by paramedics. We calculated the sensitivity, specificity, positive predictive value, negative predictive value, and the difference in aLVO probabilities with a positive or negative prehospital scale test (ΔPaLVO) for each scale for mild (NIHSS 0-4), intermediate (NIHSS 5-9), moderate (NIHSS 10-14), and severe deficits (NIHSS≥15). RESULTS: Among 1033 patients with suspected stroke, 119 (11.5%) had an aLVO, of whom 19 (16.0%) had mild, 25 (21.0%) had intermediate, 30 (25.2%) had moderate, and 45 (37.8%) had severe deficits. The scales had low sensitivity and positive predictive value in patients with mild-intermediate deficits, and poor specificity, negative predictive value, and accuracy with moderate-severe deficits. Positive results achieved the highest ΔPaLVO in patients with mild deficits. Negative results achieved the highest ΔPaLVO with severe deficits, but the probability of aLVO with a negative result in the severe range was higher than with a positive test in the mild range. CONCLUSIONS: Commonly-used prehospital stroke scales show variable performance across the range of deficit severity. Probability of aLVO remains high with a negative test in severely affected patients. Studies reporting prehospital stroke scale performance should be appraised in the context of the NIHSS distribution of their samples
- …