Discriminatory processor sharing queues with stationary ergodic service times and the performance of TCP in overload

In a recent paper, Bonald and Roberts (2001) [6] studied non-persistent TCP connections in transient overload conditions, under the assumption that all connections have the same round-trip times. In this paper our goal is to develop theoretical tools that will enable us to relax this assumption and obtain explicit expressions for the rate of growth of the number of connections at the system, the rate at which TCP connections leave the system, as well as the time needed for the completion of a connection. To that end, we model the system as a discriminatory processor sharing (DPS) system which we analyze under very mild assumptions on the probability distributions related to different classes of arrivals: we only assume that the arrival rates of connections exist, and that the amount of information transmitted during a connection of a given type forms a stationary ergodic sequence. We then proceed to obtain explicit expressions for the growth rate of the number of connections at the DPS system for several specific probability distributions. We check through simulations the applicability of our queueing results for modeling TCP connections sharing a bottleneck.     

Capacitance-conductance investigation on the phase transitions in Ga nanoparticles

We have reported on coupled capacitance-conductance measurements on Ga nanoparticles embedded in vitreous matrices. The melting of nanoparticles was clearly detected as an abrupt increase in the capacitance vs. temperature scans. The influence of the embedding matrix and of the frequency of the applied field on the dielectric response was checked. The presence of a hysteresis cycle between melting and solidification has been detected. The technique allows the identification of the various solid phases of confined Ga.     

On the capacity of binary and Gaussian channels withrun-length-limited inputs

Bounds on the capacity of binary symmetric channels and additive Gaussian channels with run-length-limited two-level (binary, bipolar) inputs are presented, and their tightness is demonstrated for some cases. Stationary input sequences, which do not degrade capacity, are considered when deriving the bounds. Lower bounds on the magnetic recording density for a simple continuous-time recording model incorporating a minimal intertransition constraint are evaluated for soft and hard decisions. A superiority of about 1.5 dB in signal-to-noise ratio is observed for the soft-decision scheme     

Robust closed-loop control of isometric muscle force usingpulsewidth modulation

The design of feedback controllers to accurately and robustly regulate the properties of electrically stimulated muscle is considered. Reliable, precise control is necessary for the development of neuroprosthetic devices to improve gradation and repeatability of force. A digital closed-loop controller has been developed which regulates muscle force by modulating the pulsewidth of a constant-amplitude electrical simulation pulse train. This controller has been evaluated in slow- and fast-twitch muscles (cat soleus and plantaris) in acute experiments. In isometric tests, it was found to regulate muscle force with low sensitivity to modeling errors and disturbances while satisfying stability, repeatability, linearity, and step/ramp response criteria over a wide range of commands     

Behavioral reversal of lithium effects by four inositol isomers correlates perfectly with biochemical effects on the PI cycle: depletion by chronic lithium of brain inositol is specific to hypothalamus, and inositol levels may be abnormal in postmortem brain from bipolar patients

The inositol depletion hypothesis of lithium (Li) action has been criticized, because depletion of inositol after chronic Li treatment has not been reproducible, effects of inositol to reverse Li-induced behaviors occurred also with epi-inositol, a unnatural isomer, and because inositol is ubiquitous in brain and hard to relate to the pathogenesis of affective disorder. Therefore, we review our studies showing that lithium depletion of brain inositol occurs chronically in the hypothalamus, a region not previously examined; that behavioral effects of four different inositol isomers including epi-inositol correlate perfectly with their biochemical effects; and that inositol in postmortem human brain is reduced by 25% in frontal cortex of bipolars and suicides as compared with controls. Because inositol in postmortem brain is reduced and not increased in bipolar patients, the relationship between inositol, lithium, and affective disorder is complex.     

On the efficiency of quantization-based integration methods for building simulation

Models describing energy consumption, heating, and cooling of buildings usually impose difficulties to the numerical integration algorithms used to simulate them. Stiffness and the presence of frequent discontinuities are among the main causes of those difficulties, that become critical when the models grow in size. Quantized State Systems (QSS) methods are a family of numerical integration algorithms that can efficiently handle discontinuities and stiffness in large models. For this reason, they are promising candidates for overcoming the mentioned problems. Based on this observation, this article studies the performance of QSS methods in some systems that are relevant to the field of building simulation. The study includes a performance comparison of different QSS algorithms against state-of-the-art classic numerical solvers, showing that the former can be more than one order of magnitude faster.     

Determination of the ice dielectric permittivity using the data ofthe test in Antarctica of the ground-penetrating radar for Mars'98mission

A ground-penetrating radar will be integrated inside the guiderope ballast of the Mars'98 balloon mission. A prototype of this impulse system working in the 5-15 MHz band was tested close to Dumont d'Urville, the French Antarctic Station, in February 1993. The authors obtained a large set of profiles in cold ice with a glacier thickness from 200 to about 900 m. For each depth, the measured echoes are very clear with a good signal-to-noise ratio (SNR). In this paper, the authors firstly describe the performances of the radar and they study the electromagnetic propagation in the Antarctica glacier. This knowledge allows them to use the frequency wavenumber migration to focus the signal, to increase the SNR and to rebuild an image of the subsurface. The migration process gives a good estimation of the real part of the permittivity (i.e., the velocity). The fact that the signal comes from different depths is used to measure the imaginary part of the permittivity which defines the ice attenuation. The spectral analysis gives its frequency dependence