New paradoxical games based on Brownian ratchets

Based on Brownian ratchets, a counter-intuitive phenomenon has recently emerged -- namely, that two losing games can yield, when combined, a paradoxical tendency to win. A restriction of this phenomenon is that the rules depend on the current capital of the player. Here we present new games where all the rules depend only on the history of the game and not on the capital. This new history-dependent structure significantly increases the parameter space for which the effect operates.Comment: 4 pages, 3 eps figures, revte

Minimal Brownian Ratchet: An Exactly Solvable Model

We develop an exactly-solvable three-state discrete-time minimal Brownian ratchet (MBR), where the transition probabilities between states are asymmetric. By solving the master equations we obtain the steady-state probabilities. Generally the steady-state solution does not display detailed balance, giving rise to an induced directional motion in the MBR. For a reduced two-dimensional parameter space we find the null-curve on which the net current vanishes and detailed balance holds. A system on this curve is said to be balanced. On the null-curve, an additional source of external random noise is introduced to show that a directional motion can be induced under the zero overall driving force. We also indicate the off-balance behavior with biased random noise.Comment: 4 pages, 4 figures, RevTex source, General solution added. To be appeared in Phys. Rev. Let

Parrondo's games as a discrete ratchet

We write the master equation describing the Parrondo's games as a consistent discretization of the Fokker--Planck equation for an overdamped Brownian particle describing a ratchet. Our expressions, besides giving further insight on the relation between ratchets and Parrondo's games, allow us to precisely relate the games probabilities and the ratchet potential such that periodic potentials correspond to fair games and winning games produce a tilted potential.Comment: 4 pages, 3 figure

Mechanisms for the Increased Fatigability of the Lower Limb in People with Type 2 Diabetes

Fatiguing exercise is the basis of exercise training and a cornerstone of management of type 2 diabetes mellitus (T2D), however, little is known about the fatigability of limb muscles and the involved mechanisms in people with T2D. The purpose was to compare fatigability of knee extensor muscles between people with T2D and controls without diabetes and determine the neural and muscular mechanisms for a dynamic fatiguing task. Seventeen people with T2D (10 men, 7 women: 59.6{plus minus}9.0 years) and 21 age-, BMI- and physical activity-matched controls (11 men, 10 women: 59.5{plus minus}9.6 years) performed 120 high-velocity concentric contractions (1 contraction/3 s) with a load equivalent to 20% maximal voluntary isometric contraction (MVIC) torque with the knee extensors. Transcranial magnetic stimulation (TMS) and electrical stimulation of the quadriceps were used to assess voluntary activation and contractile properties. People with T2D had larger reductions than controls in power during the fatiguing task (39.9{plus minus}20.2% vs. 28.3{plus minus}16.7%, P2=0.364, P=0.002). Although neural mechanisms contributed to fatigability, contractile mechanisms were responsible for the greater knee extensor fatigability in men and women with T2D compared with healthy controls

The discovery of a low mass, pre-main-sequence stellar association around gamma Velorum

We report the serendipitous discovery of a population of low mass, pre-main sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the low mass stars are truly associated, are approximately coeval and that both are at distances between 360-490 pc, disagreeing at the 2 sigma level with the recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance estimates. Our results clearly have implications for the physical parameters of the gamma^{2} Vel system, but also offer an exciting opportunity to investigate the influence of high mass stars on the mass function and circumstellar disc lifetimes of their lower mass PMS siblings.Comment: Monthly Notices of the Royal Astronomical Society, Letters - in pres

Human engineering design criteria study Final report

Human engineering design criteria for use in designing earth launch vehicle systems and equipmen

Reduced up-regulation of gene expression in response to elevated temperatures in the mid-Atlantic population of Calanus finmarchicus

Abstract Climate change is affecting numerous species worldwide, including dominant and important copepods of the genus Calanus. Despite the growing body of studies that examine effects of climate change stressors on Calanus species, comparative intraspecific studies are lacking. Importantly, acclimatization and genetic adaptation can modify the stress response, thus leading to a differential response of separated populations to the same stressor. The molecular and physiological responses of a C. finmarchicus population from the mid-Atlantic, with an in situ temperature of 8.5 °C, were investigated under experimental thermal conditions of 0 °C, 5 °C, 10 °C, 15 °C, and 20 °C for durations of 3 h and 6 days. This experimental set-up mirrored previously published experiments conducted on C. finmarchicus at the northern limit of its distribution allowing a comparison between two populations. The greatest physiological response, assessed as fecal pellet production, was seen after 3 h exposure at 10 °C and 15 °C, and after 6 days exposure at 5 °C, 10 °C and 15 °C. Molecular response was assessed by the change in expression of 5 selected genes: hsp70_2, dnaja1, nap 1l1, rps11, and gdh. Only two out of the five genes (gdh and nap1l1) showed significant up-regulation with increased temperature and duration of exposure. These findings differ from the results obtained in the northern population where all 5 genes were differently expressed. Overall, the results suggest population-specific response to temperature in C. finmarchicus, however determining the source of such variation (genetic adaptation or acclimatization) requires more detailed studies

A Preliminary Discussion of the Kinematics of BHB and RR Lyrae Stars near the North Galactic Pole

The radial velocity dispersion of 67 RR Lyrae variable and blue horizontal branch (BHB) stars that are more than 4 kpc above the galactic plane at the North Galactic Pole is 110 km/sec and shows no trend with Z (the height above the galactic plane). Nine stars with Z < 4 kpc show a smaller velocity dispersion (40 +/-9 km/sec) as is to be expected if they mostly belong to a population with a flatter distribution. Both RR Lyrae stars and BHB stars show evidence of stream motion; the most significant is in fields RR2 and RR3 where 24 stars in the range 4.0 < Z < 11.0 kpc have a mean radial velocity of -59 +/- 16 km/sec. Three halo stars in field RR 2 appear to be part of a moving group with a common radial velocity of -90 km/sec. The streaming phenomenon therefore occurs over a range of spatial scales. The BHB and RR Lyrae stars in our sample both have a similar range of metallicity (-1.2 < [Fe/H] < -2.2). Proper motions of BHB stars in fields SA 57 (NGP) and the Anticenter field (RR 7) (both of which lie close to the meridional plane of the Galaxy) show that the stars that have Z 4 kpc have a Galactic V motion that is < -200 km/sec and which is characteristic of the halo. Thus the stars that have a flatter distribution are really halo stars and not members of the metal-weak thick-disk.Comment: Accepted for publication in the March 1996 AJ. 15 pages, AASTeX V4.0 latex format (including figures), 2 eps figures, 2 separate AASTeX V4.0 latex table

Hyper-Fractionated Radiotherapy for Soft Tissue Sarcoma: Results of the Second Study of Hyper-Fractionated Radiotherapy

Purpose and Method. Hyper-fractionated radiotherapy for treatment of soft tissue sarcomas is designed to deliver a higher total dose of radiation without an increase in late normal tissue damage. In a previous study at the Royal Marsden Hospital, a total dose of 75 Gy using twice daily 1.25 Gy fractions resulted in a higher incidence of late damage than conventional radiotherapy using 2 Gy daily fractions treating to a total of 60 Gy. The current trial therefore used a lower dose per fraction of 1.2 Gy and lower total dose of 72 Gy, with 60 fractions given over a period of 6 weeks