632 research outputs found
Services within a busy period of an M/M/1 queue and Dyck paths
We analyze the service times of customers in a stable M/M/1 queue in
equilibrium depending on their position in a busy period. We give the law of
the service of a customer at the beginning, at the end, or in the middle of the
busy period. It enables as a by-product to prove that the process of instants
of beginning of services is not Poisson. We then proceed to a more precise
analysis. We consider a family of polynomial generating series associated with
Dyck paths of length 2n and we show that they provide the correlation function
of the successive services in a busy period with (n+1) customers
Extreme Environment Effects on Cognitive Functions: A Longitudinal Study in High Altitude in Antarctica.
This paper focuses on the impact of long-term Antarctic conditions on cognitive processes. Behavioral responses and event-related potentials were recorded during an auditory distraction task and an attention network paradigm. Participants were members of the over-wintering crew at Concordia Antarctic Research Station. Due to the reduced partial pressure of oxygen this environment caused moderate hypoxia. Beyond the hypoxia, the fluctuation of sunshine duration, isolation and confinement were the main stress factors of this environment. We compared 6 measurement periods completed during the campaign. Behavioral responses and N1/MMN (mismatch negativity), N1, N2, P3, RON (reorientation negativity) event-related potential components have been analyzed. Reaction time decreased in both tasks in response to repeated testing during the course of mission. The alerting effect increased, the inhibition effect decreased and the orienting effect did not change in the ANT task. Contrary to our expectations the N2, P3, RON components related to the attentional functions did not show any significant changes. Changes attributable to early stages of information processing were observed in the ANT task (N1 component) but not in the distraction task (N1/MMN). The reaction time decrements and the N1 amplitude reduction in ANT task could be attributed to sustained effect of practice. We conclude that the Antarctic conditions had no negative impacts on cognitive activity despite the presence of numerous stressors
The effective bandwidth problem revisited
The paper studies a single-server queueing system with autonomous service and
priority classes. Arrival and departure processes are governed by marked
point processes. There are buffers corresponding to priority classes,
and upon arrival a unit of the th priority class occupies a place in the
th buffer. Let , denote the quota for the total
th buffer content. The values are assumed to be large, and
queueing systems both with finite and infinite buffers are studied. In the case
of a system with finite buffers, the values characterize buffer
capacities.
The paper discusses a circle of problems related to optimization of
performance measures associated with overflowing the quota of buffer contents
in particular buffers models. Our approach to this problem is new, and the
presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in
Stochastic Model
Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements
Coupling losses were studied in composite tapes containing superconducting
material in the form of two separate stacks of densely packed filaments
embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry
is quite favorable for studying the coupling currents and in particular the
role of superconducting bridges between filaments. By using a.c. susceptibility
technique, the electromagnetic losses as function of a.c. magnetic field
amplitude and frequency were measured at the temperature T = 77 K for two tapes
with different matrix composition. The length of samples was varied by
subsequent cutting in order to investigate its influence on the dynamics of
magnetic flux penetration. The geometrical factor which takes into
account the demagnetizing effects was established from a.c. susceptibility data
at low amplitudes. Losses vs frequency dependencies have been found to agree
nicely with the theoretical model developed for round multifilamentary wires.
Applying this model, the effective resistivity of the matrix was determined for
each tape, by using only measured quantities. For the tape with pure silver
matrix its value was found to be larger than what predicted by the theory for
given metal resistivity and filamentary architecture. On the contrary, in the
sample with a Ag/Mg alloy matrix, an effective resistivity much lower than
expected was determined. We explain these discrepancies by taking into account
the properties of the electrical contact of the interface between the
superconducting filaments and the normal matrix. In the case of soft matrix of
pure Ag, this is of poor quality, while the properties of alloy matrix seem to
provoke an extensive creation of intergrowths which can be actually observed in
this kind of samples.Comment: 20 pages 11 figure, submitted to Superconductor Science and
Technolog
Casimir force between planes as a boundary finite size effect
The ground state energy of a boundary quantum field theory is derived in
planar geometry in D+1 dimensional spacetime. It provides a universal
expression for the Casimir energy which exhibits its dependence on the boundary
conditions via the reflection amplitudes of the low energy particle
excitations. We demonstrate the easy and straightforward applicability of the
general expression by analyzing the free scalar field with Robin boundary
condition and by rederiving the most important results available in the
literature for this geometry.Comment: 10 pages, 2 eps figures, LaTeX2e file. v2: A reference is added, some
minor modifications made to clarify the text. v3: 9 pages, 3 eps figures,
LaTeX2e file, revtex style. Paper throughly restructured and rewritten. Much
more details are given, but essential results and conclusions are unchanged.
Version accepted for publicatio
Distinction of apple cultivars according to their mal D 1 allergen coding genes using PCR technique
Apple is one of the most important fruit grown and consumed in the temperate climate region. About 2% of the European population suffers from several allergenic reactions after consumption. Presence of 7 members of Mal d 1 gene family occurring in some apples was examined by PCR. The Mal d 1.01 and 1.02 genes could be detected from 91% and 79% of apple cultivars, respectively, due to the high degree of conservative regions. The Mal d 1.04 gene has 4 functional varieties and 2 pseudo-alleles, so it is highly variable. The PCR amplifi cation with Mal d 1.06 primers gave one or two fragments with different sizes. The electrophoretic pattern is a suitable means to select apple cultivars according to their low, medium, or high Mal d 1 allergen content. Florina apple showed the single 154 bp allele, which is responsible for the small Mal d 1 allergen content in homozygote form..
Several samples gave weak signal or did not give any fragment-band on the gel, so Mal d 1.07 and 1.08 genes might have more varieties. Regarding the Mal d 1.09 gene we have found that it has conservative sequences in different apple cultivars and does not have too many varieties
Casimir effect in the boundary state formalism
Casimir effect in the planar setting is described using the boundary state
formalism, for general partially reflecting boundaries. It is expressed in
terms of the low-energy degrees of freedom, which provides a large distance
expansion valid for general interacting field theories provided there is a
non-vanishing mass gap. The expansion is written in terms of the scattering
amplitudes, and needs no ultraviolet renormalization. We also discuss the case
when the quantum field has a nontrivial vacuum configuration.Comment: 11 pages. Proceedings contribution of talk given at the Workshop on
Quantum Field Theory under the Influence of External Conditions (QFEXT07),
University of Leipzig, September 16-21, 2007. To appear in J. Phys.
- …