7,695 research outputs found
Efficient simulation of relativistic fermions via vertex models
We have developed an efficient simulation algorithm for strongly interacting
relativistic fermions in two-dimensional field theories based on a formulation
as a loop gas. The loop models describing the dynamics of the fermions can be
mapped to statistical vertex models and our proposal is in fact an efficient
simulation algorithm for generic vertex models in arbitrary dimensions. The
algorithm essentially eliminates critical slowing down by sampling two-point
correlation functions and it allows simulations directly in the massless limit.
Moreover, it generates loop configurations with fluctuating topological
boundary conditions enabling to simulate fermions with arbitrary periodic or
anti-periodic boundary conditions. As illustrative examples, the algorithm is
applied to the Gross-Neveu model and to the Schwinger model in the strong
coupling limit.Comment: 5 pages, 4 figure
Virtual Entanglement and Reconciliation Protocols for Quantum Cryptography with Continuous Variables
We discuss quantum key distribution protocols using quantum continuous
variables. We show that such protocols can be made secure against individual
gaussian attacks regardless the transmission of the optical line between Alice
and Bob. This is achieved by reversing the reconciliation procedure subsequent
to the quantum transmission, that is, using Bob's instead of Alice's data to
build the key. Although squeezing or entanglement may be helpful to improve the
resistance to noise, they are not required for the protocols to remain secure
with high losses. Therefore, these protocols can be implemented very simply by
transmitting coherent states and performing homodyne detection. Here, we show
that entanglement nevertheless plays a crucial role in the security analysis of
coherent state protocols. Every cryptographic protocol based on displaced
gaussian states turns out to be equivalent to an entanglement-based protocol,
even though no entanglement is actually present. This equivalence even holds in
the absence of squeezing, for coherent state protocols. This ``virtual''
entanglement is important to assess the security of these protocols as it
provides an upper bound on the mutual information between Alice and Bob if they
had used entanglement. The resulting security criteria are compared to the
separability criterion for bipartite gaussian variables. It appears that the
security thresholds are well within the entanglement region. This supports the
idea that coherent state quantum cryptography may be unconditionally secure.Comment: 18 pages, 6 figures. Submitted to QI
Proposal for a loophole-free Bell test using homodyne detection
We propose a feasible optical setup allowing for a loophole-free Bell test
with efficient homodyne detection. A non-gaussian entangled state is generated
from a two-mode squeezed vacuum by subtracting a single photon from each mode,
using beamsplitters and standard low-efficiency single-photon detectors. A Bell
violation exceeding 1% is achievable with 6-dB squeezed light and an homodyne
efficiency around 95%. A detailed feasibility analysis, based upon the recent
generation of single-mode non-gaussian states, confirms that this method opens
a promising avenue towards a complete experimental Bell test.Comment: 4 pages RevTex, 2 figure
Interactive digital signal processor
The Interactive Digital Signal Processor (IDSP) is examined. It consists of a set of time series analysis Operators each of which operates on an input file to produce an output file. The operators can be executed in any order that makes sense and recursively, if desired. The operators are the various algorithms used in digital time series analysis work. User written operators can be easily interfaced to the sysatem. The system can be operated both interactively and in batch mode. In IDSP a file can consist of up to n (currently n=8) simultaneous time series. IDSP currently includes over thirty standard operators that range from Fourier transform operations, design and application of digital filters, eigenvalue analysis, to operators that provide graphical output, allow batch operation, editing and display information
Excitation Enhancement of a Quantum Dot Coupled to a Plasmonic Antenna
Plasmonic antennas are key elements to control the luminescence of quantum
emitters. However, the antenna's influence is often hidden by quenching losses.
Here, the luminescence of a quantum dot coupled to a gold dimer antenna is
investigated. Detailed analysis of the multiply excited states quantifies the
antenna's influence on the excitation intensity and the luminescence quantum
yield separately
ERP Implementation in Portugal: Interpreting Dimensions of Power
We use the dimensions of power framework (Hardy and Leiba-O\u27Sullivan 1998) to study an ERP implementation in a Portuguese small/medium sized enterprise (SME). In this study, we found that while the ERP implementation coincided with a great shift of power within the firm, it should not be considered the main driver of the episodic power shift. Instead, the ERP can be seen as a tool chosen and used to formalize and complete the shift in power for this SME. Our findings provide evidence of the usefulness of the dimensions of power framework in understanding complex organizational power issues in ERP implementations. Given the nature of the firm and the context, such findings are specific to an emerging economy
Zinc Extraction potential of two common crop plants, Nicotiana tabacum and Zea mays
A field study was conducted to investigate the efficiency of Zn phytoextraction by Nicotiana tabacum and Zea mays from a soil that had been artificially contaminated by different amounts of ZnSO4 (0, 50, 150, 350, 750 and 1550 mg kg−1 soil) 10 years prior to the present cropping. Increased NaNO3-extractable Zn in soil translated well into shoot concentrations (dry matter) in plants. Zn uptake by Z. mays increased linearly with increasing NaNO3-extractable Zn in soil, while for N. tabacum the increase could be described by a Langmuir isotherm. While Z. mays showed no significant decrease in biomass production up to the highest contamination level in soil, N. tabacum responded with a reduction of plant growth of about 50% compared with control plants at the highest Zn concentrations in soil. Maximum removal of Zn was 13 kg ha−1 y−1 with Z. mays and 11 kg ha−1 y−1 with N. tabacum. Calculated time required to reduce soil Zn from 350 to 150 mg kg−1 was about 55 years for N. tabacum and about 63 years for Z. mays at a soil pH of 4.8. At higher soil pH of 6.0 calculated decontamination time was about 87 years for N. tabacum and more than 200 years for Z. mays. Only small amounts of Zn were translocated into the seeds of N. tabacum and cobs of Z. mays. Therefore, corn cobs of Z. mays could be safely used for fodder and the seeds of N. tabacum, which are rich in oil, for industrial purposes, e.g. in the paint industr
The PAS-domain kinase PASKIN: a new sensor in energy homeostasis
Abstract.: The PAS domain kinase PASKIN, also termed PAS kinase or PASK, is an evolutionarily conserved potential sensor kinase related to the heme-based oxygen sensors of nitrogen-fixing bacteria. In yeast, the two PASKIN homologs link energy flux and protein synthesis following specific stress conditions. In mammals, PASKIN may regulate glycogen synthesis and protein translation. Paskin knock-out mice do not show any phenotype under standard animal husbandry conditions. Interestingly, these mice seem to be protected from the symptoms of the metabolic syndrome when fed a high-fat diet. Energy turnover might be increased in specific PASKIN-deficient cell types under distinct environmental conditions. According to the current model, binding of a putative ligand to the PAS domain disinhibits the kinase domain and activates PASKIN auto- and target phosphorylation. Future research needs to be conducted to elucidate the nature of the putative ligand and the molecular mechanisms of downstream signalling by PASKI
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