710 research outputs found
On departure process in the batch arrival queue with single vacation and setup time
A single-server queueing system of MX/G/1 type with unlimited buffer size is considered. Whenever the system becomes empty, the server takes a single compulsory vacation that is independent of the arrival process. The service of the first customer after the vacation is preceded by a random setup time. We distinguish two cases of the evolution of the system: when the setup time begins after the vacation only, or if it begins at once when the first group of customers enters. In the paper we investigate the departure process h(t) that at any fixed moment t takes on a random value equal to the number of customers completely served before t. An explicit representation for Laplace Transform of probability generating function of departure process is derived and written down by means of transforms of four crucial input distributions of the system and factors of a certain factorization identity connected with them. The results are obtained using the method consisting of two main stages: first we study departure process on a single vacation cycle for an auxiliary system and direct the analysis to the case of the system without vacations, applying the formula of total probability; next we use the renewal-theory approach to obtain a general formula
On transient queue-size distribution in the batch arrival system with the N-policy and setup times
In the paper the queueing system with the -policy and setup times is considered. An explicit formula for the Laplace
transform of the transient queue-size distribution is derived using
the approach consisting of few steps. Firstly, a "special\u27\u27
modification of the original system is investigated and, using the
formula of total probability, the analysis is reduced to the case
of the corresponding system without limitation in the service. Next,
a renewal process generated by successive busy cycles is used to
obtain the general result. Sample numerical computations
illustrating theoretical results are attached as well
Central mode and soft mode behavior in PbMg1/Nb2/3O3 relaxor ferroelectric
The relaxor ferroelectric PbMg1/Nb2/3O3 was investigated by means of
broad-band dielectric and Fourier Transform Infrared (FTIR) transmission
spectroscopy in the frequency range from 1 MHz to 15 THz at temperatures
between 20 and 900 K using PMN films on infrared transparent sapphire
substrates. While thin film relaxors display reduced dielectric permittivity at
low frequencies, their high frequency intrinsic or lattice response is shown to
be the same as single crystal/ceramic specemins. It was observed that in
contrast to the results of inelastic neutron scattering, the optic soft mode
was underdamped at all temperatures. On heating, the TO1 soft phonon followed
the Cochran law with an extrapolated critical temperature equal to the Burns
temperature of 670 K and softened down to 50 cm-1. Above 450 K the soft mode
frequency leveled off and slightly increased above the Burns temperature. A
central mode, describing the dynamics of polar nanoclusters appeared below the
Burns temperature at frequencies near the optic soft mode and dramatically
slowed down below 1 MHz on cooling below room temperature. It broadened on
cooling, giving rise to frequency independent losses in microwave and lower
frequency range below the freezing temperature of 200 K. In addition, a new
heavily damped mode appeared in the FTIR spectra below the soft mode frequency
at room temperature and below. The origin of this mode as well as the
discrepancy between the soft mode damping in neutron and infrared spectra is
discussed.Comment: 7 pages with 7 figures, submitted to Phys. Rev.
Non-stationary departure process in a batch-arrival queue with finite buffer capacity and threshold-type control mechanism
summary:Non-stationary behavior of departure process in a finite-buffer -type queueing model with batch arrivals, in which a threshold-type waking up -policy is implemented, is studied. According to this policy, after each idle time a new busy period is being started with the th message occurrence, where the threshold value is fixed. Using the analytical approach based on the idea of an embedded Markov chain, integral equations, continuous total probability law, renewal theory and linear algebra, a compact-form representation for the mixed double transform (probability generating function of the Laplace transform) of the probability distribution of the number of messages completely served up to fixed time is obtained. The considered queueing system has potential applications in modeling nodes of wireless sensor networks (WSNs) with battery saving mechanism based on threshold-type waking up of the radio. An illustrating simulational and numerical study is attached
High-frequency dielectric spectroscopy of batio3 core - silica shell nanocomposites: Problem of interdiffusion
Three types of BaTiO3 core - amorphous nano-shell composite ceramics were
processed from the same core-shell powder by standard sintering, spark-plasma
sintering and two-step sintering techniques and characterized by XRD, HRSEM and
broad-band dielectric spectroscopy in the frequency range 10^3 - 10^13 Hz
including the THz and IR range. The samples differed by porosity and by the
amount of interdiffusion from the cores to shells, in correlation with their
increasing porosity. The dielectric spectra were also calculated using suitable
models based on effective medium approximation. The measurements revealed a
strong dielectric dispersion below the THz range, which cannot be explained by
the modeling, and whose strength was in correlation with the degree of
interdiffusion. We assigned it to an effect of the interdiffusion layers,
giving rise to a strong interfacial polarization. It appears that the
high-frequency dielectric spectroscopy is an extremely sensitive tool for
detection of any gradient layers and sample inhomogeneities even in dielectric
materials with negligible conductivity
Los alumnos prefieren diferentes estrategias didácticas de la enseñanza de las ciencias en función de sus características motivacionales
We carried out empirical research into the relationship between students' motivational pattems and their preferences for different teaching procedures in science education. According to the results obtained, students tend to prefer those teaching procedures and strategies that allow their motivational needs to be met and reject those conflicting with them
Neutron scattering study of ferroelectric Sn2P2S6 under pressure
Ferroelectric phase transition in the semiconductor Sn2P2S6 single crystal
has been studied by means of neutron scattering in the pressure-temperature
range adjacent to the anticipated tricritical Lifshitz point (p=0.18GPa,
T=296K). The observations reveal a direct ferroelectric-paraelectric phase
transition in the whole investigated pressure range (0.18 - 0.6GPa). These
results are in a clear disagreement with phase diagrams assumed in numerous
earlier works, according to which a hypothetical intermediate incommensurate
phase extends over several or even tens of degrees in the 0.5GPa pressure
range. Temperature dependence of the anisotropic quasielastic diffuse
scattering suggests that polarization fluctuations present above TC are
strongly reduced in the ordered phase. Still, the temperature dependence of the
(200) Bragg reflection intensity at p=0.18GPa can be remarkably well modeled
assuming the order-parameter amplitude growth according to the power law with
logarithmic corrections predicted for a uniaxial ferroelectric transition at
the tricritical Lifshitz point
Analysing central metabolism in ultra-high resolution: at the crossroads of carbon and nitrogen
BACKGROUND: Cancer cell metabolism can be characterised by adaptive metabolic alterations, which support abnormal proliferative cell growth with high energetic demand. De novo nucleotide biosynthesis is essential for providing nucleotides for RNA and DNA synthesis, and drugs targeting this biosynthetic pathway have proven to be effective anticancer therapeutics. Nevertheless, cancers are often able to circumvent chemotherapeutic interventions and become therapy resistant. Our understanding of the changing metabolic profile of the cancer cell and the mode of action of therapeutics is dependent on technological advances in biochemical analysis. SCOPE OF REVIEW: This review begins with information about carbon- and nitrogen-donating pathways to build purine and pyrimidine moieties in the course of nucleotide biosynthesis. We discuss the application of stable isotope resolved metabolomics to investigate the dynamics of cancer cell metabolism and outline the benefits of high-resolution accurate mass spectrometry, which enables multiple tracer studies. CONCLUSION: With the technological advances in mass spectrometry that allow for the analysis of the metabolome in high resolution, the application of stable isotope resolved metabolomics has become an important technique in the investigation of biological processes. The literature in the area of isotope labelling is dominated by (13)C tracer studies. Metabolic pathways have to be considered as complex interconnected networks and should be investigated as such. Moving forward to simultaneous tracing of different stable isotopes will help elucidate the interplay between carbon and nitrogen flow and the dynamics of de novo nucleotide biosynthesis within the cell
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