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Perseverance refers to the ability that individuals show in the process of overcoming failure repeatedly and achieving success. The present study aimed to investigate how many stories about struggling role models undergraduates with a low level of perseverance need to read to effectively improve their perseverance after experiencing failure. Undergraduates with high and low levels of perseverance who had experienced failure were randomly assigned to read 5 struggle stories or 5 achievement stories of role models. They were asked to report their confidence in success, their emotional experience, and their persistent intentions after experiencing failure (i.e., their initial report after reading 0 stories) and then again after reading each story. The results showed that the participants' initially reported level of confidence in success improved after reading 1 struggle story of a role model and further improved after reading 5 struggle stories of role models. Furthermore, the participants' initially reported level of positive emotions increased after reading 1 struggle story or 1 achievement story of a role model, and the positive effects began to level off after reading 4 struggle stories or 4 achievement stories of role models. The participants' initially reported persistent intentions improved after reading 5 struggle stories of role models. These findings reveal that undergraduates can benefit from reading struggle stories of role models regardless of their perseverance levels. Undergraduates' confidence in success and their emotional experience can be improved more quickly than their persistent intentions after experiencing failure.

As a set of photocatalyst and its co-catalyst with exceptional photo-degradation performance, rGO exhibits a conspicuous board-spectrum sensitization effect to TiO2. It has been widely recognized by studies in the field of water treatment that, their synergistic can also markedly complement short carrier lifetime and other shortcomings of TiO2. Over the years, research conducted on TiO2-rGO binary composite material manifests its wide modifiable space for seeking a better degradation performance and a higher solar availability. We presents an overview study on the latest modification methods of the TiO2-rGO binary composite material and divide them into categories. This article focuses on the four of them as follows: morphology and crystalline engineering, doping modification, semiconductor ternary combination, noble-metal decoration. Furthermore, the in-depth degradation mechanism and novel structure design of the modified TiO2-rGO binary composite materials are reviewed. Ongoing difficulties and promising opportunities have been summarized and expected in this article, aiming to guide the design and study of the future photo-degradation nanomaterial.

The purpose of this study aimed to analyze the process of online collaborative problem solving (CPS) via brain-to-brain synchrony (BS) at the problem-understanding and problem-solving stages. Aiming to obtain additional insights than traditional approaches (survey and observation), BS refers to the synchronization of brain activity between two or more people, as an indicator of interpersonal interaction or common attention. Thirty-six undergraduate students participated. Results indicate the problem-understanding stage showed a higher level of BS than the problem-solving stage. Moreover, the level of BS at the problem-solving stage was significantly correlated with task performance. Groups with all high CPS skill students had the highest level of BS, while some of the mixed groups could achieve the same level of BS. BS is an effective indicator of CPS to group performance and individual interaction. Implications for the online CPS design and possible supports for the process of online CPS activity are also discussed.

Recently, the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties. Here, we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport, scanning tunnelling microscope (STM) measurements and band structure calculations. For a bulk sample, it exhibits large magneto-resistance (MR) and Shubnikov–de Hass oscillations in ρxx and a series of Hall plateaus in ρxy at low temperatures. Meanwhile, the MoTe2 thin films were intensively investigated with thickness dependence. For samples, without encapsulation, an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness. In such thin films, we also observed a suppression of the MR and weak anti-localization (WAL) effects. We attributed these effects to disorders originated from the extrinsic surface chemical reaction, which is consistent with the density functional theory (DFT) calculations and in-situ STM results. In contrast to samples without encapsulated protection, we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride (h-BN) film protection. Our results indicate that the metallic or superconducting behavior is its intrinsic state, and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.

Vapor compression heat pump is of great significance to space thermal control. It can effectively regulate the temperature of electronic devices to ensure proper operation. Weightlessness is a significant factor affecting the operation. Weightlessness test of vapor compression heat pump was conducted to investigate the weightless effect on its performance. Weightlessness test was achieved by free fall on a platform 60 m above the ground. The tests of continuous weightlessness and single stroke of weightlessness were presented and analyzed. The results showed that the weightlessness decreased the evaporative heat transfer performance and enhanced the condensation heat transfer performance. It is then advisable to increase heat transfer area of the evaporator in the design of future vapor compression heat pumps, and the design of condensers could still be based on the routine method adopted in ground applications. This part of experimental data for space application of vapor compression heat pump is expected to be of great significance.

Feature matching, which refers to establishing reliable feature correspondences between two images of the same scene, is a critical prerequisite in a wide range of remote sensing tasks including environment monitoring, multispectral image fusion, image mosaic, change detection, map updating. In this paper, we propose a method for robust feature matching and apply it to the problem of remote sensing image registration. We start by creating a set of putative feature matches which can contain a number of unknown false matches, and then focus on mismatch removal. This is formulated as a robust regression problem, and we customize a robust estimator, namely the Gaussian field criterion, to solve it. The robust criterion can handle both linear and nonlinear image transformations. In the linear case, we use a general homography to model the transformation, while in the nonlinear case, the non-rigid functions located in a reproducing kernel Hilbert space are considered, and a regularization term is added to the objective function to ensure its well-posedness. Moreover, we apply a sparse approximation to the non-rigid transformation and reduce the computational complexity from cubic to linear. Extensive experiments on various natural and remote sensing images show the effectiveness of our approach, which is able to yield superior results compared to other state-of-the-art methods.

Pristine graphene has low thermoelectric performance due to its ultra-high thermal conductivity and a low Seebeck coefficient, the latter of which results from the zero-band gap of graphene. To improve the thermoelectric performance of graphene-based materials, various methods have been proposed to open a band gap in graphene. Graphene antidot lattices is one of the most effective methods to reach this goal by patterning periodic nano- or sub-1-nm pores (antidots) across graphene. In high-porosity graphene antidot lattices, charge carriers mainly flow through the narrow necks between pores, forming a comparable case as graphene nanoribbons. This will open a geometry-dependent band gap and dramatically increase the Seebeck coefficient. The antidots also strongly scatter phonons, leading to a dramatically reduced lattice thermal conductivity to further enhance the thermoelectric performance. In computations, the thermoelectric figure of merit of a graphene antidot lattices was predicted to be around 1.0 at 300 K but experimental validation is still required. The electrical conductivity and Seebeck coefficient of graphene antidot lattices on various substrates including SiO2, SiC and hexagonal boron nitride were measured. The antidots were drilled with a focused ion beam or reactive ion etching.

Knowledge of soil moisture is essential for soil conservation and efficient water resources management especially related to control nonpoint-source pollution. Soil topographic indices (STI) are often used to understand the soil moisture patterns in landscapes and make effective landscape management decisions. This study assessed the relationships between soil moisture measurements and STI values in two study sites in North-central New Jersey, USA. The soil moisture measurements were taken in these study sites using a time domain reflectometry probe during thirteen sampling events between April 2013 and July 2015. The STI values at the sampling points were derived from a 3-m LiDAR digital elevation model and SSURGO soil database. The Spearman’s correlation analysis based on these data in all sampling points identified a significant positive correlation between soil moisture and STI. Strong positive relationships between soil moisture and STI were also identified when using binned data to eliminate the impacts of unevenness in data distribution and the impacts of micro-variations in topography, vegetation, soil compaction, and instrumental errors. The linear mixed modeling results revealed significant and positive impacts of STI and precipitation, and significant but negative impacts of temperature on soil moisture. The degrees of these effects vary across two study sites, which reflect the complex and dynamic interactions among soils, topography and climate in landscapes that affect soil moisture. Given the stochastic nature of climate factors such as precipitation and temperature, the static STI would be a reliable factor to predict soil moisture patterns in the landscape. The findings support various STI-based conservation planning efforts in New Jersey and beyond such as targeting hydrologically sensitive areas for natural resources protection and preservation and best management practice implementation.

Vapor compression refrigeration is considered as ideal miniature cooling system for miniature electronic systems and portable cooling systems. Many applications of the miniature refrigeration system are working under the situations (such as aviation field, individual combat system and automobile air conditioning, etc.) that exist bump, tilt, and even flip, which will severely degrade the performance of the miniature refrigeration system. In order to study the influence of compressor’s tilt angle on refrigeration system, a test bench was built and the performance experiments were made. The results show that the compressor’s tilt angle has a great impact on the refrigeration system performance. When the compressor worked at the maximum tilt angle of 60°, COP-c and COP-h of the system change periodically. When the compressor works in full load, the maximum tilt angle for compressor is 20°. When the compressor tilt angle is 15°, there is an optimal amount of refrigerant charge, and corresponding COP-c and COP-h reach the maximum of 2.9 and 3.9, respectively.

Glucose is a promising feedstock for hydrogen production but the existing microbial electrolysis process suffers from low efficiency. Here we show a process for hydrogen production using an integrated device consisting of a liquid-catalyst fuel cell (LCFC) stack and a polymer exchange membrane electrolytic cell (PEMEC). Glucose that cannot be directly used in traditional fuel cell was used as both the fuel to power the LCFC and the hydrogen sources. Different from simple combination of two independent units, the LCFC and PEMEC in our device are dependant one on another by using a SHAREDCELL, and all electrolytes in both fuel cell and electrolyzer are self-regenerated without using external electricity. As a result, feed stock of glucose was converted to pure hydrogen in cathode, and carbon dioxide in anode. The net reaction of the process is that glucose decomposes to hydrogen and carbon dioxide under thermal heating at ~85 oC. Glucose is a promising feedstock for hydrogen production but the existing microbial reactors are expensive and suffer from low efficiencies. Here, the authors show an improved self-powered liquid catalyst fuel cell with a polymer-exchange membrane and polyoxometalate to catalyse glucose to hydrogen.

The concentrations and characteristics of 16 polycyclic aromatic hydrocarbons (PAHs) in 48 oil samples randomly collected from 30 catering services that employ six cooking methods were quantified via high-performance liquid chromatography (HPLC). These 16 PAHs were detected in almost all of the samples. The levels of Σ16PAHs, Σ4PAHs, benzo[a]pyrene (BaP), and total BaP equivalents (ΣBaPeq) for the six cooking methods exceeded the legal limit. The concentrations of Σ4PAHs were approximately 9.5 to 16.4 times the legal limit proposed by the European Commission (Off J Eur Union 215:4-8, 2011), and the level of BaP exceeded the national standard in China by 4.7- to 10.6-fold, particularly in oil from fried foods. Low molecular weight PAHs (LMW PAHs) were predominant in fried food oil from different catering services and accounted for 94.8 % of these oils, and the ΣBaPeq of the high molecular weight PAHs (HMW PAHs) was 11.5-fold higher than that of the LMW PAHs. The concentrations of Σ16PAHs (3751.9-7585.8 μg/kg), Σ4PAHs (144.6-195.7 μg/kg), BaP (79.7-135.8 μg/kg), and ΣBaPeq (231.0-265.4 μg/kg) were highest in the samples from fast food restaurants/buffets (FB), followed by those from fried food stalls (FS) and then cooking restaurants/cafeterias (RC). The results of this study suggest that the government should strengthen control and supervision of PAH contamination in food and edible oils.

Objective To observe the clinical effect of tuina reduction manipulation on leg length discrepancy and lumbosacral pain due to sacroiliac joint subluxation.

We report on noise and thermal conductance measurements taken in order to determine an upper bound on the performance of graphene as a terahertz photon detector. The main mechanism for sensitive terahertz detection in graphene is bolometric heating of the electron system. To study the properties of a device using this mechanism to detect terahertz photons, we perform Johnson noise thermometry measurements on graphene samples. These measurements probe the electron-phonon behavior of graphene on silicon dioxide at low temperatures. Because the electron-phonon coupling is weak in graphene, superconducting contacts with large gap are used to confine the hot electrons and prevent their out-diffusion. We use niobium nitride leads with a $T_\mathrm{c}\approx 10$ K to contact the graphene. We find these leads make good ohmic contact with very low contact resistance. Our measurements find an electron-phonon thermal conductance that depends quadratically on temperature above 4 K and is compatible with single terahertz photon detection., Comment: 6 Pages, 4 Figures, Conference Proceedings from LTD-15

Two Cd(II) coordination polymers, namely, {[Cd(L1)(chdc)]·(CH3CN)·(H2O)2}n (1) and [Cd(L2)Cl2]n (2) (L1 = 1,4-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene, L2 = 1,2-bis(5,6-dimethylbenzimidazole-1-ylmethyl)benzene, H2chdc = 1,4-cyclohexanedicarboxylic acid) have been obtained by hydrothermal methods and characterized by IR, TG, elemental analysis, XPRD and single crystal structure analysis. The Cd(II) atom has a distorted octahedral coordination geometry in 1 and a roughly square-pyramidal coordination geometry in 2. Polymer 1 possesses a two-dimensional (2D) flat (6,3) network constructed with L1 and chdc bridging ligands. Polymer 2 displays a one-dimensional (1D) loop-like chain structure bridged by chlorine anions and L2 ligand, which is further arranged into a 2D supramolecular layer through face-to-face π–π stacking interactions. The luminescent properties of the polymers 1 and 2 were investigated in the solid-state. Two new coordination polymers of cadmium have been synthesized by different bis(benzimidazole) ligands. Both the complexes are characterized by X-ray single crystal structure, thermal and photoluminescence study.

HAISHEN is a long-ranged and highly maneuverable AUV which has two operating modes: glider mode and flapping-foil propulsion mode. As part of the vehicle development, a three-dimensional mathematical model of the conceptual vehicle was developed on the assumption that HAISHEN has a rigid body with two independently controlled oscillating hydrofoils. A flapping-foil model was developed based on the work done by Georgiades et al. (2009). Effect of controllable hydrofoils on the vehicle stable motion performance was studied theoretically. Finally, a dynamics simulation of the vehicle in both operating modes is created in this paper. The simulation demonstrates that: (1) in the glider mode, owing to the independent control of the pitch angle of each hydrofoil, HAISHEN travels faster and more efficiently and has a smaller turning radius than conventional fix-winged gliders; (2) in the flapping-foil propulsion mode, HAISHEN has a high maneuverability with a turning radius smaller than 15 m and a forward motion velocity about 1.8 m/s; (3) the vehicle is stable under all expected operating conditions.

Two new dinuclear copper(II) complexes, Cu2(L1)4(mal)2(H2O)2 (1) (L1 = 5,6-dimethylbenzimidazole, mal = malonate), Cu2(L2)2(pydca)2·4H2O (2) (L2 = 1,5-bis(5,6-dimethylbenzimidazole)pentane, pydca = pyridine-2,6-dicarboxylate) have been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The Cu(II) atoms in 1 and 2 both have square pyramidal coordination geometry. In 1, the two similar mononuclear structures are linked by π–π stacking as well as multiple hydrogen bonding interactions to generate a 2D supramolecular layer, while complex 2 is connected with two different patterns of π–π stacking and hydrogen bonding interactions into a 3D supramolecular network. The catalytic activities of 1 and 2 for the degradation of Congo red have been investigated.

To demonstrate the variation and affecting factors of dissolved oxygen under different aeration strategies in polluted urban river sediment, simulation systems constructed with collected sediment and in situ overlaying water were aerated up or beneath the sediment-water interface 6 h day−1 for 15 days. The results showed that aeration greatly altered the spatial pattern of DO in overlying water regardless of the way of treatment. Within the first 5 min of aeration, DO in overlying water increases rapidly from 0.86–3.13 mg L−1 to the saturated range of 6.12–8.14 mg L−1. During the first 5 days, aeration to water costed 5 min to reach the highest DO, while aeration to sediment costed 30 min to reach a lower highest level of DO in overlaying water. Analysis showed that DO was significantly negatively correlated with NO2 −-N and COD Mn , suggesting that DO was synergistically consumed by biochemical processes of organic matter degradation and nitrification. Aeration to sediment (ES group) and aeration to water (EW group) differently influenced nitrification and organic matter degradation. After daily aeration treatment, nitrification was the main oxygen-depleting process in EW group, especially after the action of the second stage of nitrification, where organic matter was probably largely degraded during aeration. However, in ES group, DO was consumed by both organic matter oxidation and nitrification processes.

Two one-dimensional Cd(II) coordination polymers constructed by ribbon-like molecules, {[Cd(L1)2(NO3)]·NO3} n (1) (L1 = 1,3-bis(5,6-dimethylbenzimidazol-1-yl)benzene) and [Cd(L2)2(NO3)2] n (2) (L2 = 1,3-bis(benzimidazol-1-yl)benzene) have been obtained through assembly of the two structurally similar flexible bis(benzimidazole)-based ligands and cadmium nitrate tetrahydrate. The cadmium(II) centers display different coordination environments with trigonal-bipyramidal geometry in 1, and a octahedral geometry in 2. Weak C–H···O interactions in 1 result in a two-dimensional supramolecular layer; two π–π interactions are present in 2 forming a three-dimensional supramolecular network structure. The solid state fluorescence properties of 1 and 2 were investigated.

The double-hydrophilic multiblock copolymers poly(ethylene glycol)-b-poly((2-acrylamido-2-methyl propanesulfonic sodium) (PEG-b-PAMPSNa) with different PEG and PAMPSNa ratio have been synthesized. The copolymers were characterized by FTIR, 1H-NMR, elemental analysis, thermogravimetric analysis (TGA) and Gel permeation chromatography coupled with multi-angle light scattering laser light scattering (GPC-MALLS). According to the results, it was seen that the compositions had obvious influences to the characteristics of the copolymers. With more PEG content in the copolymers, the molecular weights and thermal stability increased, and the copolymers chain structures were more flexible. The solution properties of the copolymers were studied by dynamic light scattering (DLS), which also have great relationship with the copolymers compositions. And PEG-b-PAMPSNa was used as a crystal growth modifier to control the crystallization of BaSO4 in its aqueous solution. The morphologies and sizes of BaSO4 crystals can be well controlled by the copolymer. With the increasing concentration, the copolymer assembled in water and interacted with inorganic particles on the crystal faces, which is concerned with the controlling of crystal growth in solution.

In graphene, which is an atomic layer of crystalline carbon, two of the distinguishing properties of the material are the charge carriers two-dimensional and relativistic character. The first experimental evidence of the two-dimensional nature of graphene came from the observation of a sequence of plateaus in measurements of its transport properties in the presence of an applied magnetic field. These are signatures of the so-called integer quantum Hall effect. However, as a consequence of the relativistic character of the charge carriers, the integer quantum Hall effect observed in graphene is qualitatively different from its semiconductor analogue. As a third distinguishing feature of graphene, it has been conjectured that interactions and correlations should be important in this material, but surprisingly, evidence of collective behaviour in graphene is lacking. In particular, the quintessential collective quantum behaviour in two dimensions, the fractional quantum Hall effect (FQHE), has so far resisted observation in graphene despite intense efforts and theoretical predictions of its existence. Here we report the observation of the FQHE in graphene. Our observations are made possible by using suspended graphene devices probed by two-terminal charge transport measurements. This allows us to isolate the sample from substrate-induced perturbations that usually obscure the effects of interactions in this system and to avoid effects of finite geometry. At low carrier density, we find a field-induced transition to an insulator that competes with the FQHE, allowing its observation only in the highest quality samples. We believe that these results will open the door to the physics of FQHE and other collective behaviour in graphene., Comment: 14 pages, 3 figures

The present study aimed to explore the protective effect of endogenous sulfur dioxide (SO2) in the development of monocrotaline (MCT)-induced pulmonary hypertension (PH) in rats. Forty Wistar rats were randomly divided into the MCT group receiving MCT treatment, the MCT+L-aspartate-β-hydroxamate (HDX) group receiving MCT plus HDX treatment, the MCT+SO2 group receiving MCT plus SO2 donor treatment, and the control group. Mean pulmonary artery pressure (mPAP) and structural changes in pulmonary arteries were evaluated. SO2 content, aspartate aminotransferase activity, and gene expression were measured. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), reduced glutathione (GSH), oxidized glutathione, and malondialdehyde (MDA) levels were assayed. In the MCT-treated rats, mPAP and right ventricle/(left ventricle+septum) increased significantly (P

Aim: The present study was designed to explore the endogenous production and localization of the sulfur dioxide (SO 2 )/aspartate aminotransferase pathway in vascular tissues of rats and to examine its vasorelaxant effect on isolated aortic rings, as well as the possible mechanisms. Methods: The content of SO 2 in the samples was determined by using high performance liquid chromatography with fluorescence detection. Aspartate aminotransferase activity and its gene expression were measured by an enzymatic method and quantitative RT–PCR, respectively. Aspartate aminotransferase mRNA location in aorta was detected by in situ hybridization. The vasorelaxant effect of SO 2 on isolated aortic rings of the rats was investigated in vitro . L-type calcium channel blocker, nicardipine, and L-type calcium channel agonist, Bay K8644, were used to explore the mechanisms by which SO 2 relaxed the aortic rings. Results: Aorta had the highest SO 2 content among the vascular tissues tested (P 2 derivatives (Na 2 SO 3 /NaHSO 3 ) relaxed isolated artery rings slightly, whereas higher doses (1–12 mmol/L) relaxed rings in a concentration-dependent manner. Pretreatment with nicardipine eliminated the vasorelaxant response of the norepinephrine-contracted rings to SO 2 completely. Incubation with nicardipine or SO 2 derivatives successfully prevented vasoconstriction induced by Bay K8644. Conclusion: Endogenous SO 2 and its derivatives have a vasorelaxant function, the mechanisms of which might involve the inhibition of the L-type calcium channel.

The discovery of graphene1,2 raises the prospect of a new class of nanoelectronic devices based on the extraordinary physical properties3,4,5,6 of this one-atom-thick layer of carbon. Unlike two-dimensional electron layers in semiconductors, where the charge carriers become immobile at low densities, the carrier mobility in graphene can remain high, even when their density vanishes at the Dirac point. However, when the graphene sample is supported on an insulating substrate, potential fluctuations induce charge puddles that obscure the Dirac point physics. Here we show that the fluctuations are significantly reduced in suspended graphene samples and we report low-temperature mobility approaching 200,000 cm2 V−1 s−1 for carrier densities below 5 × 109 cm−2. Such values cannot be attained in semiconductors or non-suspended graphene. Moreover, unlike graphene samples supported by a substrate, the conductivity of suspended graphene at the Dirac point is strongly dependent on temperature and approaches ballistic values at liquid helium temperatures. At higher temperatures, above 100 K, we observe the onset of thermally induced long-range scattering. The novel electronic properties of graphene can be compromised when it is supported on an insulating substrate. However, suspended graphene samples can display low-temperature mobility values that cannot be attained in semiconductors or non-suspended graphene, and the conductivity approaches ballistic values at liquid-helium temperatures.

In order to solve the problems of link layer retransmission and packet fragment strategies for IEEE 802.11, this paper proposes a variable packet TCPfriendly rate control (VPTFRC) scheme for streaming media transmission over wireless local area network (WLAN) by researching on the policy of packet size adjustment in transport layer based on the minimum retransmit-delay constraint. Unlike other proposals, this process considers the impact of wireless packet error ratio (PER) on the packet size adjustment and the performance of rate control. Simulation results demonstrate that our proposed process can simultaneously achieve higher throughput, better fairness, shorter transmission delay and less jitter than TFRC. Among them, the ratio of delay, jitter and packet loss rate can reach a maximum improvement ratio of 58%, 42% and 85% respectively.

Many systems in nature, glasses, interfaces and fractures being some examples, cannot equilibrate with their environment, which gives rise to novel and surprising behaviour such as memory effects, ageing and nonlinear dynamics. Unlike their equilibrated counterparts, the dynamics of out-of- equilibrium systems is generally too complex to be captured by simple macroscopic laws. Here we investigate a system that straddles the boundary between glass and crystal: a Bragg glass formed by vortices in a superconductor. We find that the response to an applied force evolves according to a stretched exponential, with the exponent reflecting the deviation from equilibrium. After the force is removed, the system ages with time and its subsequent response time scales linearly with its age (simple ageing), meaning that older systems are slower than younger ones. We show that simple ageing can occur naturally in the presence of sufficient quenched disorder. Moreover, the hierarchical distribution of timescales, arising when chunks of loose vortices cannot move before trapped ones become dislodged, leads to a stretched-exponential response., 16 pages, 5 figures

Most proxy caches for streaming videos do not cache the entire video but only a portion of it. This is partly due to the large size of video objects. Another reason is that the popularity of different parts of a video can be different, e.g., the prefix is generally more popular. Therefore, the development of efficient cache mechanisms requires an understanding of the internal popularity characteristics of streaming videos. This paper has two major contributions. Firstly, we analyze two 6-month long traces of RTSP video requests recorded at different streaming video servers of an entertainment video-on-demand provider, and show that the traces provide evidence that the internal popularity of the majority of the most popular videos obeys a k-transformed Zipf-like distribution. Secondly, we propose a caching algorithm which exploits this empirical internal popularity distribution. We find that this algorithm has similar performance compared with fine-grained caching but requires significantly less state information.

Recent empirical studies of the real traffic measurement show that the traditional traffic models cannot capture the character of long-range dependence of the traffic. And many computer simulations said that this character has large influences on the network performance. So fractal or self-similar models are more suitable to describe the modern traffic. But there is still little known about the performance of the multiplexer under self-similar traffic. In this paper, a quasi-self-similar traffic model (QSSP) is proposed. Using this model, the upper bond of the cell loss rate and multiplexing gain of the multiplexer are gotten when there are N i.i.d. QSSP inputs. If the sources have different parameters, an efficient numerical algorithm to get this bond is proposed. Simulations indicate that our analysis is correct and accurate.

Due to large size and different popularity for different part of the video, most proxy caches for streaming medias cache only a part of the video. Thus, an accurate understanding on the internal popularity distribution of media objects in streaming applications is very important for the development of efficient cache mechanisms. This letter shows that the internal popularity of popular streaming media obeys a k-transformed Zipf-like distribution through analyzing two 6-month long traces recorded at different streaming video servers of an entertainment video-on-dem and provider. This empirical model can be used to design an efficient caching algorithm.