Effect of molecular weight on the fracture surface energy of poly(methyl methacrylate) in cleavage

By the radiolysis of poly(methylmethacrylate) (PMMA), the fracture surface energy () was determined at room temperature as a function of viscosity average molecular weight (¯M _v). Using a modified parallel cleavage technique, results showed that decreased more than two orders of magnitude with decreasing molecular weight. In the high molecular weight region (¯M _v10⁵), (1×10⁵ erg cm^–2) was relatively insensitive to polymer chain length; whereas for 2.5×10⁴¯M _v 1×10⁵, was strongly dependent on molecular weight. A linear regression analysis in the range ¯M _v=2 to 2.25×10³ indicated that a truly glassy Griffith material was approached for which 750 erg cm^–2. The results confirm the sigmoidal dependence of on molecular weight tested in notched tension. The apparent independence which variations in crack velocity have on with decreasing ¯M _v is shown and explained in terms of the increasingly brittle character of PMMA. Problems associated with the measurement and interpretation of experimental data are considered, particularly with respect to the lower ¯M _v regions.     

Inadequate cervical mucus--a cause of "idiopathic" infertility

The purpose of this study was to investigate and treat a group of patients referred for "idiopathic" infertility in whom no apparent cause for infertility, apart from inadequate cervical mucus, was found. Hormone investigations revealed that these patients could be divided into two groups: those with low sex steroid profiles despite apparent ovulation, and a second group with normal sex steroid profiles. All patients were treated with ovulation-inducing agents in an attempt to produce "controlled" ovarian hyperstimulation and an improved cervical mucus. Four of six patients conceived. The rationale behind the use of ovulation-inducing agents in this situation is discussed.     

嵌入式操作系统管理汇聚应用

当今许多复杂的嵌入式系统要求信号处理和信号控制两种功能.过去这两种功能一直属于DSP和微控制器(MCU)两种独立的器件.然而,汇聚处理器的推出改变了这种现状,将DSP和MCU两种功能集成到一种灵活体系结构中,典型的代表有ADI公司的B1ackfin处理器系列.     

Relaying protocols for two colocated users

We consider a wireless network where a remote source sends information to one of two colocated users, and where the second user can serve as a relay. The source's transmission is subjected to quasi-static flat Rayleigh fading, while the transmission of the relay experiences a fixed amplitude gain with a uniform random phase, capturing its close proximity to the destination. All communications share the same time/bandwith resources, and perfect channel state information is known only to the receivers. We propose relaying protocols which are based on Wyner-Ziv quantization at the relay, and demonstrate their high efficiency (in terms of expected throughput) with respect to previously reported relaying schemes based on amplify-and-forward and decode-and-forward. A salient feature of these protocols is that the relay need not know the actual fading gain experienced by the destination in order to perform the quantization. We also consider a hybrid amplify-quantize-decode-and-forward scheme which exhibits superior performance.     

Observations of Aggressive Children During Peer Provocation and With a Best Friend.

Observational methods were used to examine aggressive children's peer relations in 2 contexts: when being teased by a peer and when interacting with a best friend. Because aggressive children may have more difficulty than nonaggressive children in both peer contexts, the authors also examined whether relations between behaviors across contexts varied as a function of aggression. Results indicated that aggression was related to children's behavior when provoked. Children's behavior when provoked was associated with fewer positive and more negative interactions with their best friend, particularly for aggressive children. Results are discussed with respect to social norms in middle childhood and informing interventions for aggressive children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Magnetic flux array for spontaneous magnetic reconnection experiments

Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A(phi). From the measured A(phi), the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A(phi) at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.     

Which Languages Have 4-Round Zero-Knowledge Proofs?

We show that if a language L has a 4-round, black-box, computational zero-knowledge proof system with negligible soundness error, then [`(L)] ? MA\bar{L}\in \mathsf{MA}. Assuming the polynomial hierarchy does not collapse, this means in particular that NP-complete languages do not have 4-round zero-knowledge proofs with black-box simulation.     

Wikiometrics: a Wikipedia based ranking system

We present a new concept—Wikiometrics—the derivation of metrics and indicators from Wikipedia. Wikipedia provides an accurate representation of the real world due to its size, structure, editing policy and popularity. We demonstrate an innovative “mining” methodology, where different elements of Wikipedia – content, structure, editorial actions and reader reviews – are used to rank items in a manner which is by no means inferior to rankings produced by experts or other methods. We test our proposed method by applying it to two real-world ranking problems: top world universities and academic journals. Our proposed ranking methods were compared to leading and widely accepted benchmarks, and were found to be extremely correlative but with the advantage of the data being publically available.