Integral Fluctuation Relations for Entropy Production at Stopping Times

A stopping time $T$ is the first time when a trajectory of a stochastic process satisfies a specific criterion. In this paper, we use martingale theory to derive the integral fluctuation relation $\langle e^{-S_{\rm tot}(T)}\rangle=1$ for the stochastic entropy production $S_{\rm tot}$ in a stationary physical system at stochastic stopping times $T$. This fluctuation relation implies the law $\langle S_{\rm tot}(T)\rangle\geq 0$, which states that it is not possible to reduce entropy on average, even by stopping a stochastic process at a stopping time, and which we call the second law of thermodynamics at stopping times. This law implies bounds on the average amount of heat and work a system can extract from its environment when stopped at a random time. Furthermore, the integral fluctuation relation implies that certain fluctuations of entropy production are universal or are bounded by universal functions. These universal properties descend from the integral fluctuation relation by selecting appropriate stopping times: for example, when $T$ is a first-passage time for entropy production, then we obtain a bound on the statistics of negative records of entropy production. We illustrate these results on simple models of nonequilibrium systems described by Langevin equations and reveal two interesting phenomena. First, we demonstrate that isothermal mesoscopic systems can extract on average heat from their environment when stopped at a cleverly chosen moment and the second law at stopping times provides a bound on the average extracted heat. Second, we demonstrate that the average efficiency at stopping times of an autonomous stochastic heat engines, such as Feymann's ratchet, can be larger than the Carnot efficiency and the second law of thermodynamics at stopping times provides a bound on the average efficiency at stopping times.Comment: 37 pages, 6 figure

Solid Propellant Power Systems for Normal and Emergency Space Operations

The ability of man to function safely both inside and out of his spacecraft will become even more critical after his pioneering flights such as Gemini and Apollo are completed. As greater numbers of astronauts make flights of long duration, survival may well be a function of a number of extravehicular activities such as routine vehicle inspection, emergency maintenance and repair. erection of structures and platforms, and rescue operations. Current systems remain bulky, heavy, and a possible source of hazard and malfunction. The solid-propellant space power systems examined here are small, light, manually or automatically operated, and have the capability not only to propel and stabilize man in space, but provide a means of power to do an extremely wide variety of critical functions outside or within a spacecraft. It has often been stated that there is no need to replace a working system. The authors of this paper are in full agreement with this statement. Let us assume for purposes of illustration a simplified spacecraft which requires only two systems for its operation, one in the nose which is hydraulic, and another in the tail which is electrical. Both are well designed and completely workable. As long as they are capable of performing their required function and as long as they are capable of growth to meet additional mission requirements, there should be no valid reason to replace either by a solid-propellant hot gas system. But let us consider further. In the event of a failure of either system during a flight, the parts of one system cannot be used in a repair of the other. It would be very surpris - ing if the motors, switches, etc. of the electrical system could be substituted in any way for any of the valves and cylinders of the various hydraulic devices and vice versa. If, however, both systems were replaced with a compatible gas generator powered system, a failure in either end of the spacecraft could use parts and prime movers frorn the other. The present philosophy for space-borne systems and components imposes as criteria of design extremely high standards of operational reliability and there is no quarrel with this doctrine. However, high reliability from the standpoint of completion of a manned space mission ·does not necessarily imply complete maintenance- free reliability during the entire operating life of the various systems involved. We are dealing here with a vehicle containing a crew of thinking, random decision making, non-linear operating, human beings rather than an inanimate object which is capable of performing only the actions for which it has been pre-programmed. At the present time, crew members of space vehicles perform a variety of maintenance functions which enhance the operability of themselves and their vehicles. Such simple non-programmed act ions as tuning a radio or adjusting a thermostat can be considered as part of the maintenance functions. Bad communications? A pilot will naturally and instinctively tune his command receiver for increased performance or change to another communications channel where reception might be better. Too hot? A crew member turns down the thermostat on his suit a couple of notches to compensate for the extra heat load caused by unplanned exertion

Data Access for LIGO on the OSG

During 2015 and 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) conducted a three-month observing campaign. These observations delivered the first direct detection of gravitational waves from binary black hole mergers. To search for these signals, the LIGO Scientific Collaboration uses the PyCBC search pipeline. To deliver science results in a timely manner, LIGO collaborated with the Open Science Grid (OSG) to distribute the required computation across a series of dedicated, opportunistic, and allocated resources. To deliver the petabytes necessary for such a large-scale computation, our team deployed a distributed data access infrastructure based on the XRootD server suite and the CernVM File System (CVMFS). This data access strategy grew from simply accessing remote storage to a POSIX-based interface underpinned by distributed, secure caches across the OSG.Comment: 6 pages, 3 figures, submitted to PEARC1

Inkoop huisartsenzorg nog een gok

Verzekeraars willen grip op de kwaliteit die zorgverleners leveren. De mogelijkheden hiervoor zijn bij huisartsen veel beperkter dan bij bijvoorbeeld fysiotherapeuten. Er is behoefte aan objectieve criteria om kwaliteit van zorg in kaart te brengen