DxHash: A Scalable Consistent Hash Based on the Pseudo-Random Sequence

Consistent hasing has played a fundamental role as a data router and a load balancer in various fields, such as distributed database, cloud infrastructure, and peer-to-peer network. However, the existing consistent hashing schemes can't meet the requirements simultaneously, including full consistency, scalability, small memory footprint, low update time and low query complexity. Thus, We propose DxHash, a scalable consistent hashing algorithm based on the pseudo-random sequence. For the scenario of distributed storage, there are two optimizations based on DXHash are proposed. First, the Weighted DxHash can adjust the workloads on arbitrary nodes. Second, the Asymmetric Replica Strategy (ARS) is combining the replica strategy in distributed storage with the scaleup process to improve the availability of the system and reduce the remapping rate. The evaluation indicates that compared with the state-of-art works, DxHash achieves significant improvements on the 5 requirements. Even with 50% failure ratio, DxHash still can complete 16.5 million queries per second. What's more, the two optimizations both achieve their own results

WLFC: Write Less in Flash-based Cache

Flash-based disk caches, for example Bcache and Flashcache, has gained tremendous popularity in industry in the last decade because of its low energy consumption, non-volatile nature and high I/O speed. But these cache systems have a worse write performance than the read performance because of the asymmetric I/O costs and the the internal GC mechanism. In addition to the performance issues, since the NAND flash is a type of EEPROM device, the lifespan is also limited by the Program/Erase (P/E) cycles. So how to improve the performance and the lifespan of flash-based caches in write-intensive scenarios has always been a hot issue. Benefiting from Open-Channel SSDs (OCSSDs), we propose a write-friendly flash-based disk cache system, which is called WLFC (Write Less in the Flash-based Cache). In WLFC, a strictly sequential writing method is used to minimize the write amplification. A new replacement algorithm for the write buffer is designed to minimize the erase count caused by the evicting. And a new data layout strategy is designed to minimize the metadata size persisted in SSDs. As a result, the Over-Provisioned (OP) space is completely removed, the erase count of the flash is greatly reduced, and the metadata size is 1/10 or less than that in BCache. Even with a small amount of metadata, the data consistency after the crash is still guaranteed. Compared with the existing mechanism, WLFC brings a 7%-80% reduction in write latency, a 1.07*-4.5* increment in write throughput, and a 50%-88.9% reduction in erase count, with a moderate overhead in read performance

Torsion for CM elliptic curves defined over number fields of degree 2p

For a prime number p, we characterize the groups that may arise as torsion subgroups of an elliptic curve with complex multiplication defined over a number field of degree 2p. In particular, our work shows that a classification in the strongest sense is tied to determining whether there exist infinitely many Sophie Germain primes

Heun and Mathieu functions as solutions of the Dirac equation

We give examples of where the Heun function exists as solutions of wave equations encountered in general relativity. While the Dirac equation written in the background of Nutku helicoid metric yields Mathieu functions as its solutions in four spacetime dimensions, the trivial generalization to five dimensions results in the double confluent Heun function. We reduce this solution to the Mathieu function with some transformations. We must apply Atiyah-Patodi-Singer spectral boundary conditions to this system since the metric has a singularity at the origin.Comment: 5 pages, Prepared for the Spanish Relativity Meeting (ERE 2007), Tenerife, Spain, 10-14 Sep 200

A Planar Laser-induced Fluorescence Study on the Effects of Unsteadiness and Fuel Lewis Number in Hydrogen Laminar Diffusion Flames

Studies on the effect of transport properties coupled with the interaction of fluid dynamics and combustion in acoustically forced laminar hydrogen jet diffusion flames have been performed using the planar laser-induced fluorescence (PLIF) technique. These unsteady diffusion flames are of particular interest because they are reproducible turbulent-like events that can be investigated to gain insight into turbulent combustion. Results reported herein add to the ongoing effort of understanding the complex transport processes taking place in the flames encountered in most modern heat-producing and power-producing devices. Fuel transport properties (i .e. fuel Lewis number, LeF) were varied by fuel dilution with various levels of helium (He) or argon (Ar). The fuel stream ofBurkeSchumann type hydrogen flames was acoustically excited by using a loudspeaker and the two-dimensional OH and temperature fields were measured. PLIF measurements were performed using an intricate two-laser, two-camera system; digital image analysis was implemented to reduce the large image data set obtained. The temperature of the unsteady flames departed significantly from the steadystate temperature as predicted by previous researchers. It was found that, regardless of LeF, unsteady He-diluted flames had maximum flame temperatures at some point during the speaker -oscillation that were always higher than the maximum temperatures of the H2-Ar flames. This was contrary to the trends seen in steady flames. An increased H2 mass flux to the flame zone in the unsteady H2-He flames was the reason for this observation since mass diffusion becomes important in the driven flames due to increased mass gradients and the difference in diffusivity of hydrogen in the diluents used. Low turbulence intensities (i.e.low frequency) allowed the flames to respond steadily to the changing flowfield. The structure of the reaction zone of unsteady flames at this low frequency was altered (i.e. stretched or compressed) slightly and, in general, these flames resembled the steady flames structurally. At high frequency, however, the flames responded to the imposed flow oscillation by considerable reaction zone stretch/compression. Results obtained from the present experiments suggest that, depending on the Lewis number, the flame temperature responds differently to the stretch imparted on the flame by the unsteady flowfield. These Lewis number effects were evidenced by both the low and high frequency flames, however, they were most obvious in the high frequency cases. The temperature of flames with LeF ~ l increased/decreased when the reaction zone thickened/thinned. On the other hand, flames with LeF \u3c l increased/decreased in temperature when the reaction zone thinned/thickened. These trends competed with the thermal and mass transport processes present in the high-curvature regions of the flames

Free-particle and harmonic-oscillator propagators in two and three dimensions

This contribution illustrates how to construct free-particle and harmonic-oscillator quantum-mechanical propagators in two and three dimensions in cartesian, and in circular and spherical coordinates, respectively, starting from the corresponding one-dimensional propagators in cartesian coordinates

Second-harmonic generation in highly textured LiNbO3 films prepared by pulsed laser deposition

LiNbO3 films have been deposited on (001) sapphire substrates by pulsed laser deposition, in an oxygen environment. Films grown at substrate temperatures of 650°C are crystalline, strongly textured, and show a degree of twining that is lower the higher the oxygen pressure is in the range of 0.5-1 Torr. Values of the nonlinear optical coefficients d33 and d31 of the films, measured via second-harmonic generation, are close to those for the bulk LiNbO3 single crystal. The dependence of both the degree of twining and the nonlinear optical response on the film thickness suggests that the films become closer to single domain for larger thickness. © 2000 American Institute of Physics.Peer Reviewe

Valoración económica del impacto ambiental generado por la descomposición anaeróbica de la paja del arroz en el parque nacional de la Albufera de Valencia

[ES] La paja del cultivo del arroz en la zona de los “Tancats” en el Parque Natural de l’Albufera puede sufrir en condiciones de humedad una degradación anaeróbica que afecta a la calidad del agua e impacta negativamente al ecosistema del lago. En el presente trabajo de valoración económica se analiza dicho impacto ocurrido entre las temporadas 2012-2013/2013-2014. Para realizar la valoración del impacto enumeramos los bienes y servicios ecosistémicos generados por el Parque Natural de l’Albufera. Una vez definidos los servicios procedemos a valorar mediante un análisis multicriterio (AMUVAM) basado en expertos, como se ven afectados cada uno de los servicios por la fermentación anaeróbica de la paja. Finalmente una vez jerarquizada la relevancia de los impactos, obtenemos a través del AMUVAM el impacto económico total.Zanchetta Chittka, JC. (2016). Valoración económica del impacto ambiental generado por la descomposición anaeróbica de la paja del arroz en el parque nacional de la Albufera de Valencia. http://hdl.handle.net/10251/72714.TFG