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51.
Multicast was one of the first "value-added" services to be developed and deployed in the Internet. In evaluating the success of multicast, if ubiquitous deployment has been the goal, multicast has not been successful. However, if widespread use of multicast as a bandwidth-saving technique has been the goal, multicast has indeed been successful. Upon closer investigation, one of the reasons for only partial success is a lack of support for service management. Multicast is particularly hard to manage interdomain where it has been less successful, but easier to manage within a domain where network administrators have more control and smaller networks to manage. In this article we survey some of the recent service management efforts, efforts that have been successful intradomain, but fall short for interdomain. In particular, we focus on important topics like monitoring multicast reachability between sources and receivers; understanding the different challenges and solutions between inter- and intradomain service management; and surveying existing solutions to determine whether multicast capability exists on an end-to-end path. Our investigation shows that while not much attention was initially given to multicast service management, more recent efforts have been successful at developing good solutions and tools. 相似文献
52.
P Rubin JP Williams PN Riggs S Bartos T Sarac R Pomerantz J Castano M Schell RM Green 《Canadian Metallurgical Quarterly》1998,40(4):929-941
BACKGROUND: Desflurane, enflurane and isoflurane can be degraded to carbon monoxide (CO) by carbon dioxide absorbents, whereas sevoflurane and halothane form negligible amounts of CO. Carbon monoxide formation is greater with drier absorbent, and with barium hydroxide, than with soda lime. The mechanism, role of absorbent composition and water, and anesthetic structures determining CO formation are unknown. This investigation examined sequential steps in anesthetic degradation to CO. METHODS: Carbon monoxide formation from anesthetics and desiccated barium hydroxide lime or soda lime was determined at equimole and equiMAC concentrations. Carbon monoxide formation from deuterium-substituted anesthetics was also quantified. Proton abstraction from anesthetics by strong base was determined by deuterium isotope exchange. A reactive chemical intermediate was trapped and identified by gas chromatography-mass spectrometry. The source of the oxygen in CO was identified by 18O incorporation. RESULTS: Desflurane,enflurane,andisoflurane(difluoromethylethyl ethers), but not sevoflurane (monofluoromethyl ether), methoxyflurane (methy-ethyl ether), or halothane (alkane) were degraded to CO. The amount of CO formed was desflurane > or = enflurane > isoflurane at equiMAC and enflurane > desflurane > isoflurane at equimole concentrations. Proton abstraction from the difluoromethoxy carbon was greater with potassium than with sodium hydroxide, but unmeasurable with barium hydroxide. Carbon monoxide formation was correlated (r = 0.95-1.00) with difluoromethoxy (enflurane > desflurane > isoflurane > or = methoxyflurane = sevoflurane = 0) but not ethyl carbon proton abstraction. Deuterium substitution on enflurane and desflurane diminished CO formation. Chemical trapping showed formation of a difluorocarbene intermediate from enflurane and desflurane. Incorporation of H2(18)O in barium hydroxide lime resulted in C18O formation from unlabeled enflurane and desflurane. CONCLUSIONS: A difluoromethoxy group is a structural requirement for haloether degradation to CO. Results are consistent with initial base-catalyzed difluoromethoxy proton abstraction (potassium > sodium hydroxide, thus greater CO formation with barium hydroxide lime vs. soda lime) forming a carbanion (reprotonated by water to regenerate the anesthetic, hence requirements for relatively dry absorbent), carbanion decomposition to a difluorocarbene, and subsequent difluorocarbene reaction to form CO. 相似文献
53.
H. Yavuz R. Altindag S. Sarac I. Ugur N. Sengun 《International Journal of Rock Mechanics and Mining Sciences》2006,43(5):767-775
Laboratory tests were conducted on 12 different carbonate rocks to investigate index properties of deteriorated rocks due to physical weathering. Physical weathering due to freeze–thaw and thermal shock action for 20 cycles, was simulated, following the procedure suggested by standard methods. Index properties, P-wave velocity, uniaxial compressive strength and Schmidt hardness, for the three series of the rock samples were determined for fresh, freeze–thaw and thermal shock conditions. It was found that the index properties of rocks treated with freeze–thaw and thermal shock decrease in varying levels with respect to initial values. A model equation predicting the index properties of rocks due to freeze–thaw and thermal shock treatment was developed by multiple regression analysis of measured data. This model explains decrease in index property of a deteriorated rock depending on its initial property and porosity of rock with the coefficients for a specific index property, given in the paper for the both freeze–thaw and thermal shock treatments. Model was validated by statistical tests. In order to estimate the index property for any cycle of freeze–thaw or thermal shock treatment, this model equation was incorporated into a previously suggested model to eliminate a decay constant required for that model to be determined for a specific rock in the laboratory. So, the final model equation could accurately predict a property of a deteriorated carbonate rock depending on treatment cycle, and initial index property and porosity. This was also proved by comparing the model with compressive strength data of a researcher for freeze–thaw cycles. 相似文献
54.
Sarac MF Wilson RM Johnston-Peck AC Wang J Pearce R Klein KL Melechko AV Tracy JB 《ACS applied materials & interfaces》2011,3(4):936-940
Vertically aligned carbon nanofibers (VACNFs) were synthesized using ligand-stabilized Ni nanoparticle (NP) catalysts and plasma-enhanced chemical vapor deposition. Using chemically synthesized Ni NPs enables facile preparation of VACNF arrays with monodisperse diameters below the size limit of thin film lithography. During pregrowth heating, the ligands catalytically convert into graphitic shells that prevent the catalyst NPs from agglomerating and coalescing, resulting in a monodisperse VACNF size distribution. In comparison, significant agglomeration occurs when the ligands are removed before VACNF growth, giving a broad distribution of VACNF sizes. The ligand shells are also promising for patterning the NPs and synthesizing complex VACNF arrays. 相似文献
55.
Ozge Sarac Mehtap Caglayan Betul Seher Uysal Ayse Guzin Taslipinar Uzel Burak Tanriverdi Nurullah Cagil 《Contact lens & anterior eye》2018,41(5):442-447
Purpose
To compare the 24 month visual, refractive, topographic and aberrometric results of the accelerated and standard corneal collagen cross-linking (CXL) in pediatric keratoconus patients.Methods
87 eyes of 64 consecutive keratoconus patients under 18 years old with 24 month follow-up period following standard or accelerated CXL were included. 38 eyes received standard CXL (3 Mw/cm2, 30?min), while 49 eyes had accelerated CXL (9?mW/cm2, 10?min). Changes in the uncorrected (UCVA) and best corrected visual acuity (BCVA), spherical equivalent (SE), manifest astigmatism (MA), corneal topographic parameters, and corneal aberrations such as spherical aberration (SA), high order aberrations (HOAs), horizontal and vertical coma were evaluated. Corneal haze was graded and progression rate was assessed.Results
The difference between baseline and 24 months postoperative UCVA, BCVA, SimK (keratometry)-1, SimK-2, Kmax, and the corneal aberrations were not significantly different between the two groups (p?>?0.05 for all). The mean reduction in thinnest corneal pachymetry from baseline to 24 months after CXL was higher in accelerated CXL group (p?=?0.007). The progression rate was 13.1% in standard and 16.3% in accelerated group (p?=?0.754). There were no differences in the grade of corneal haze between the two groups (p?=?0.249). No complications were observed in the both groups.Conclusion
The 24 month results of accelerated and standard CXL revealed that, the efficacy and safety of accelerated CXL were the same with standard CXL in pediatric keratoconus patients. As being a rapid procedure, accelerated CXL appears to be more benefical for pediatric patients. 相似文献56.
Partially neutralized poly(acrylic acid) (PAA) microspheres have been prepared by Inverse Pickering Suspension Polymerization (IPSP) using 1,2‐dichlorobenzene (DCB) and hydrophobic fumed silica nanoparticles (HFSi‐NPs) as organic dispersing media and dispersing agent respectively. As crosslinker N,N'‐methylene bisacrylamide (MBAc), as initiator potassium persulfate (KPS) and sodium metabisulfite (SMBS) redox couple were used. Neutralization degrees were adjusted using 8N NaOH solution and polymerizations were initiated at 34°C. Water/oil phase ratio was set to 1/7 for all polymerizations. Morphology of prepared dry poly(acrylic acid) beads was examined by two microscopic methods, scanning electron microscopy (SEM) and optical microscopy. Prepared microsized polymer beads were observed as smooth and spherical in shape. Effect of neutralization degree (α) varied from 70% to 90% on absorptions in both distilled water and saline solutions, absorption under load (AUL) and crosslink density (CD) results were also investigated. POLYM. ENG. SCI., 59:162–169, 2019. © 2018 Society of Plastics Engineers 相似文献
57.
Akkurt Nevzat Altan Cem Levent Sarac Mehmet Fahri 《Journal of Superconductivity and Novel Magnetism》2022,35(2):615-623
Journal of Superconductivity and Novel Magnetism - The synthesis of nanoparticles by the continuous flow process is of great interest since it allows extensive control over reaction conditions with... 相似文献
58.
The electrochemical behavior of polycarbazole (PCz) and poly(N-vinyl carbazole) P(NVCz) was investigated by means of electrochemical
impedance spectroscopy (EIS). Supporting electrolytes made from various combinations of solvents (acetonitrile and propylene
carbonate) and salts (sodium perchlorate, lithium perchlorate, and tetraethyl ammonium perchlorate) were employed in the investigation.
Information on the double layer capacitance (Cdl) and specific capacitance (Csp) of P(NVCz) was achieved by cyclic voltammetry (CV), chronoamperometry and chronopotentiometry. Carbon fiber microelectrodes
(CFME) were electrocoated by cyclic voltammetry in a monomer-free solution and displayed film thicknesses in the range ~200 nm
to ~4.8 μm. The capacitive behavior of the PCz- and P(NVCz)-coated carbon fiber microelectrodes was also investigated by CV.
The effects of the type of electrolyte and solvent on the electrochemical impedance spectroscopic data were subsequently fitted
with an ((R(C(R(Q(RW))))(CR))-equivalent circuit model to calculate the numerical values of the proposed components. The obtained
experimental Csp values for PCz/CFME and P(NVCz)/CFME, as measured in LiClO4/ACN, were 280.5 mF g−1 and 294.1 mF g−1, respectively. 相似文献
59.
In this study, the effects of the additive thiourea (TU) have been investigated under steady state/steady-flow and uniform state/uniform-flow systems with the aim of minimizing the anodic hydrogen evolution on Pd in order to increase the performance of a direct borohydride fuel cell. The fuel cell has consisted of Pd/C anode, Pt/C cathode and Na+ form Nafion membrane as the electrolyte. There has been a small improvement in peak power density and fuel utilization ratio by addition of TU (1.6 × 10−3 M) into the sodium borohydride solution; the peak power densities of 14.4 and 15.1 mW cm−2, and fuel utilization ratios of 21.6% and 23.2% have been obtained without and with TU, respectively. 相似文献
60.
Sarac AS Ozgul SE Faltz H Gencturk A Gilsing HD Schulz B 《Journal of nanoscience and nanotechnology》2010,10(12):8043-8053
Electropolymerization of 3,4-(2-benzylpropylene)-dioxythiophene (ProDOT-Bz) on (approximately 7 microm diameter) single carbon fiber microelectrodes (SCFMEs) in different electrolytes resulted the network of nanofiber structure. Electropolymerization performed in different electrolytes by using cyclovoltammetric technique. Surface morphology of coatings was investigated by Scanning Electron Microscopy (SEM), the attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used for the characterization. A linear relationship between peak currents of films with polymerization charge, and capacitances and coating thickness were obtained. The size of nanofiber network (and pores) can be controlled by the scan rate of the cyclovoltammetric process. Electrochemical impedance spectroscopic investigation of these nanostructures has been indicated the capacitive behavior of electrode system. Electrochemical Impedance Spectroscopic characterization (Capacitance) of the PProDOTBz/SCFME consisting cell was simulated at applied potential and parameters explained by equivalent circuit modeling. 相似文献