We consider the maximum disjoint paths problem and its generalization, the call control problem, in the on-line setting. In the maximum disjoint paths problem, we are given a sequence of connection requests for some communication network. Each request consists of a pair of nodes, that wish to communicate over a path in the network. The request has to be immediately connected or rejected, and the goal is to maximize the number of connected pairs, such that no two paths share an edge. In the call control problem, each request has an additional bandwidth specification, and the goal is to maximize the total bandwidth of the connected pairs (throughput), while satisfying the bandwidth constraints (assuming each edge has unit capacity). These classical problems are central in routing and admission control in high speed networks and in optical networks.We present the first known constant-competitive algorithms for both problems on the line. This settles an open problem of Garay et al. and of Leonardi. Moreover, to the best of our knowledge, all previous algorithms for any of these problems, are (logn)-competitive, where n is the number of vertices in the network (and obviously noncompetitive for the continuous line). Our algorithms are randomized and preemptive. Our results should be contrasted with the (logn) lower bounds for deterministic preemptive algorithms of Garay et al. and the (logn) lower bounds for randomized non-preemptive algorithms of Lipton and Tomkins and Awerbuch et al. Interestingly, nonconstant lower bounds were proved by Canetti and Irani for randomized preemptive algorithms for related problems but not for these exact problems. 相似文献
Central hematocrit (H) measurements are currently used to track the degree of ultrafiltration‐induced hemoconcentration with the aim to detect and prevent excessive intravascular fluid depletion during hemodialysis (HD). Failure to maintain hemodynamic stability is commonly attributed to the misinterpretation of H caused by an unaccountable increase in Fcells, the ratio of whole‐body hematocrit to H. It was the aim to examine Fcells under everyday conditions in a group of stable HD patients. Absolute plasma volume (Vp) and H were concomitantly measured during routine HD in the extracorporeal system in hourly intervals by noninvasive and continuous technology (CritLine‐Instrument‐III) and indocyanine green dye dilution to derive relative plasma volumes from Vp and H (RPVp, RPVH), respectively, and to calculate Fcells. Thirteen patients were studied during two midweek treatments (n = 26). Both absolute Vp (P < 0.05) and relative plasma volumes RPVH (P < 0.001) decreased during HD. Vp at any time point was positively correlated to RPVH (r = 0.52). Moreover, relative plasma volumes RPVH and RPVp determined by independent techniques were identical and showed negligible bias (?0.2%) but considerable limits of agreement (?15.6% to +15.3%). Fcells was stable and in the range of 0.9 ± 0.05 throughout HD and not different from the value assumed at the beginning of HD. Although Fcells remains constant in patients on routine dialysis and relative plasma volumes (RPVH and RPVp) determined by independent techniques are therefore comparable, the variability of experimental conditions during dialysis and the limited accuracy of absolute volume measurements using available technology continues to complicate the ultrafiltration control problem. 相似文献
In this paper we review some critical aspects related to interactions between cathode materials and electrolyte solutions in lithium-ion batteries. Previous results are briefly summarized, together with the presentation of new results. This review deals with the basic anodic stability of commonly-used electrolyte solutions for Li-ion batteries (mostly based on alkyl carbonate solvents). We discuss herein the surface chemistry of the following cathode materials: LiCoO2, V2O5, LiMn2O4, LiMn1.5Ni0.5O4, LiMn0.5Ni0.5O2, and LiFePO4. The methods applied included solution studies by ICP, Raman, X-ray photoelectron and FTIR spectroscopies, and electron microscopy, all in conjunction with electrochemical techniques. General phenomena are the possible dissolution of transition metal ions from these materials, which leads to changes in the active mass and a retardation in the electrode kinetics due to the formation of blocking surface films. These phenomena are significant mostly at elevated temperatures and in electrolyte solutions containing acidic species. Water-contaminated LiPF6 solutions can reach a high concentration of acidic species (e.g., HF), which is detrimental to the performance of materials such as LiCoO2 and LiFePO4. Both LiMn1.5Ni0.5O4 and LiMn0.5Ni0.5O2, even when used as nanomaterials, show a high stability in commonly-used electrolyte solutions at high temperatures. This stability is attributed to unique surface chemistry that is correlated to the presence of Ni ions in the lattice. 相似文献
The vascular endothelial growth factor (VEGF) induces pathological angiogenetic ocular diseases. It is a scientific challenge to develop carriers for the controlled release of inhibitors for VEGF present in the back of the eye domain. Carbon dots (C‐dots) functionalized with the VEGF aptamer are introduced and the hybrid nanoparticles are used for ocular nanomedicine. The C‐dots are applied as effective carriers of the anti‐VEGF aptamer across the cornea, yielding therapeutic levels upon topical administration. The hybrids show no toxicity for both in vitro and in vivo murine animal model, and further enable noninvasive intraocular concentration monitoring through the C‐dots inherent fluorescence. In addition, the hybrid C‐dots effectively inhibit VEGF‐stimulated angiogenesis in choroidal blood vessels. This inhibition is comparable to two commercially available anti‐VEGF drugs, bevacizumab and aflibercept. The hybrid aptamer‐modified C‐dots provide a versatile nanomaterial to treat age‐related macular degeneration and diabetic retinopathy. 相似文献
Scanning gate microscopy is used to determine the electrostatic limit of detection (LOD) of a nanowire (NW) based chemical sensor with a precision of sub‐elementary charge. The presented method is validated with an electrostatically formed NW whose active area and shape are tunable by biasing a multiple gate field‐effect transistor (FET). By using the tip of an atomic force microscope (AFM) as a local top gate, the field effect of adsorbed molecules is emulated. The tip induced charge is quantified with an analytical electrostatic model and it is shown that the NW sensor is sensitive to about an elementary charge and that the measurements with the AFM tip are in agreement with sensing of ethanol vapor. This method is applicable to any FET‐based chemical and biological sensor, provides a means to predict the absolute sensor performance limit, and suggests a standardized way to compare LODs and sensitivities of various sensors. 相似文献
The concatenated micro-tower (CMT) is a new configuration for concentrated solar power plants that consists of multiple mini-fields of heliostats. In each mini-field, the heliostats direct and focus sunlight onto designated points along an insulated tube, where thermal receivers are located. The heat transfer fluid, flowing through a multitude of discrete receivers, is combined and directed towards a single power block. The key advantages of CMT are its dual-axis tracking system and dynamic receiver allocation, i.e., the ability of each heliostat to direct sunrays towards receivers from adjacent mini-fields throughout the day according to their optical efficiency. Here we compare between the annual optical efficiencies of a conventional trough, large tower, and CMT configuration, all located at latitude 36 N. For each configuration, we calculated the annual optical efficiency based on the cosine factor and atmospheric transmittance. CMT’s dynamic receiver allocation provides more uniform electricity production during the day and throughout the year and improves the annual optical efficiency by 12-19% compared to conventional trough and large tower configurations. 相似文献