233 research outputs found
Absence of slow particle transport in the many-body localized phase
We analyze the saturation value of the bipartite entanglement and number entropy starting from a random product state deep in the many-body localized (MBL) phase. By studying the probability distributions of these entropies we find that the growth of the saturation value of the entanglement entropy stems from a significant reshuffling of the weight in the probability distributions from the bulk to the exponential tails. In contrast, the probability distributions of the saturation value of the number entropy are converged with system size, and exhibit a sharp cutoff for values of the number entropy which correspond to one particle fluctuating across the boundary between the two halves of the system. Our results therefore rule out slow particle transport deep in the MBL phase and confirm that the slow entanglement entropy production stems uniquely from configurational entanglement
Tandem queues with impatient customers for blood screening procedures
We study a blood testing procedure for detecting viruses like HIV, HBV and HCV. In this procedure, blood samples go through two screening steps. The first test is ELISA (antibody Enzyme Linked Immuno-Sorbent Assay). The portions of blood which are found not contaminated in this first phase are tested in groups through PCR (Polymerase Chain Reaction). The ELISA test is less sensitive than the PCR test and the PCR tests are considerably more expensive. We model the two test phases of blood samples as services in two queues in series; service in the second queue is in batches, as PCR tests are done in groups. The fact that blood can only be used for transfusions until a certain expiration date leads, in the tandem queue, to the feature of customer impatience. Since the first queue basically is an infinite server queue, we mainly focus on the second queue, which in its most general form is an S-server M=G[k;K]=S + G queue, with batches of sizes which are bounded by k and K. Our objective is to maximize the expected profit of the system, which is composed of the amount earned for items which pass the test (and before their patience runs out), minus costs. This is done by an appropriate choice of the decision variables, namely, the batch sizes and the number of servers at the second service station. As will be seen, even the simplest version of the batch queue, the M=M[k;K]=1 + M queue, already gives rise to serious analytical complications for any batch size larger than 1. These complications are discussed in detail. In view of the fact that we aim to solve realistic optimization problems for blood screening procedures, these analytical complications force us to take recourse to either a numerical approach or approximations. We present a numerical solution for the queue length distribution in theM=M[k;K]=S+M queue and then formulate and solve several optimization problems. The power-series algorithm, which is a numerical-analytic method, is also discussed
Analysis and optimization of blood testing procedures
This paper is devoted to the performance analysis and optimization of blood testing procedures. We present a queueing model of two queues in series, representing the two stages of a blood testing procedure. Service (testing) in stage 1 is performed in batches, whereas it is done individually in stage 2. Since particular elements of blood can only be stored and used within a ¿nite time window, the sojourn time of blood units in the system of two queues in series is an important performance measure, which we study in detail. We also introduce a pro¿t objective function, taking into account blood acquisition and screening costs as well as pro¿ts for blood units which were found uncontaminated and were tested fast enough. We optimize that pro¿t objective function w.r.t. the batch size and the length of the time window
A blood bank model with perishable blood and demand impatience
We consider a stochastic model for a blood bank, in which amounts of blood are offered and demanded according to independent compound Poisson processes. Blood is perishable, i.e., blood can only be kept in storage for a limited amount of time. Furthermore, demand for blood is impatient, i.e., a demand for blood may be cancelled if it cannot be satisfied soon enough. For a range of perishability functions and demand impatience functions, we derive the steady-state distributions of the amount of blood Xb kept in storage, and of the amount of demand for blood Xd (at any point in time, at most one of these quantities is positive). Under certain conditions we also obtain the fluid and diffusion limits of the blood inventory process, showing in particular that the diffusion limit process is an Ornstein-Uhlenbeck process
A Dynamic P53-MDM2 Model with Time Delay
Specific activator and repressor transcription factors which bind to specific
regulator DNA sequences, play an important role in gene activity control.
Interactions between genes coding such transcription factors should explain the
different stable or sometimes oscillatory gene activities characteristic for
different tissues. Starting with the model P53-MDM2 described into [6] and the
process described into [5] we developed a new model of this interaction.
Choosing the delay as a bifurcation parameter we study the direction and
stability of the bifurcating periodic solutions. Some numerical examples are
finally given for justifying the theoretical results.Comment: 16 pages, 12 figure
Mycobacterium tuberculosis complex DNA from an extinct bison dated 17,000 years before the present
Recycled incomplete identification procedures for blood screening
The operation of blood bank systems is characterized by two crucial factors: testing procedures and perishability. We propose a new testing procedure that we term Recycled Incomplete Identification Procedure (RIIP). In RIIP, groups of pooled blood units which are found contaminated in a so-called ELISA test are divided into smaller subgroups and again group-tested by ELISA, and so forth, until finally a so-called PCR test is conducted for those subgroups which are found clean. We analyze and optimize the performance of RIIP, maximizing the profit associated with the procedure. Our numerical results suggest that it may indeed be profitable to do several cycles at ELISA
Electronic structure of and Quantum size effect in III-V and II-VI semiconducting nanocrystals using a realistic tight binding approach
We analyze the electronic structure of group III-V semiconductors obtained
within full potential linearized augmented plane wave (FP-LAPW) method and
arrive at a realistic and minimal tight-binding model, parameterized to provide
an accurate description of both valence and conduction bands. It is shown that
cation sp3 - anion sp3d5 basis along with the next nearest neighbor model for
hopping interactions is sufficient to describe the electronic structure of
these systems over a wide energy range, obviating the use of any fictitious s*
orbital, employed previously. Similar analyses were also performed for the
II-VI semiconductors, using the more accurate FP-LAPW method compared to
previous approaches, in order to enhance reliability of the parameter values.
Using these parameters, we calculate the electronic structure of III-V and
II-VI nanocrystals in real space with sizes ranging upto about 7 nm in
diameter, establishing a quantitatively accurate description of the band-gap
variation with sizes for the various nanocrystals by comparing with available
experimental results from the literature.Comment: 28 pages, 8 figures, Accepted for publication in Phys. Rev.
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