Meso-scale analysis of FRC using a two-step homogenization approach

This paper describes the development of a two-step homogenization approach for evaluating the elastic properties of fiber reinforced concrete (FRC). For that purpose, a finite element model of an FRC unit cell was generated. Prior to the generation of the unit cell finite element model, the interface transition zones (ITZ) and the aggregates were homogenized using an analytical approach. In the first step, the properties of a spherical aggregate and its concentric ITZ layer were homogenized via an analytical procedure. Then a numerical homogenization procedure was applied to the homogenized aggregate, the mortar, and the fibers to obtain the macroscopic properties of the FRC. The suggested framework executes the multi-scale analysis of FRC structures by incorporating an original concrete unit cell generator into a commercial finite element software package intended for simulating nonlinear solid mechanical problems. The results, obtained using the presented algorithm, are in very good agreement with experimental results.     

If it looks like a spammer and behaves like a spammer,it must be a spammer: analysis and detection of microblogging spam accounts

Spam in online social networks (OSNs) is a systemic problem that imposes a threat to these services in terms of undermining their value to advertisers and potential investors, as well as negatively affecting users’ engagement. As spammers continuously keep creating newer accounts and evasive techniques upon being caught, a deeper understanding of their spamming strategies is vital to the design of future social media defense mechanisms. In this work, we present a unique analysis of spam accounts in OSNs viewed through the lens of their behavioral characteristics. Our analysis includes over 100 million messages collected from Twitter over the course of 1 month. We show that there exist two behaviorally distinct categories of spammers and that they employ different spamming strategies. Then, we illustrate how users in these two categories demonstrate different individual properties as well as social interaction patterns. Finally, we analyze the detectability of spam accounts with respect to three categories of features, namely content attributes, social interactions, and profile properties.     

A hollow-cathode copper halide laser

We have successfully operated a CuCl laser in a metal tube in a hollow-cathode configuration. An average output of 400 mW was obtained with 0.06 percent "wall plug" efficiency. Excitation was by pulse burst with a repetition rate of 1-15 kHz within the burst. Despite the use of an unsealed vacuum system and cold windows the laser was operated for more than 300 h on a single charge of CuCl. The hollow-cathode configuration appears to offer significant improvement in mechanical strength and lasant conservation over Pyrex- or quartz-walled longitudinally pumped copper halide lasers.     

Do the high-frequency indexes of HRV provide a faithful assessment of cardiac vagal tone? A critical theoretical evaluation

When spectral analysis of the heart rate (HR) signal is performed, it is quite common to attribute the HF indexes of heart rate variability (HRV) to cardiac vagal control. The paradigm underlying this attribution states that changes in cardiac vagal outflow correspond to a proportional change in respiratory sinus arrhythmia (RSA). However, recent studies have demonstrated that variations in these indexes do not necessarily reflect proportional changes in vagal tone. The current study provides a theoretical evaluation of the relationship between mean HR, RSA, and cardiac vagal tone. This evaluation is based on a theoretical model, which quantifies the differential effects of vagal blockade by a competitive muscarinic antagonist on the HF indexes of HRV. The model relies on several assumptions that reflect the basic physiology of the sinoatrial (SA) node, as well as pharmacological relations that describe agonist/antagonist equilibrium at the SA receptors. The mathematical framework of this model is the integral-pulse-frequency-modulation (IPFM) process, and its derivations lead to a specific expressions for the dependence of HF and mean HR on the level of vagal blockade. These expressions provide a new insight into the relationship between mean HR, RSA, and vagal tone, and explain conflicting experimental results previously published.     

Full-scale field tests of concrete slabs subjected to blast loads

This paper describes full-scale field explosion tests on protected and unprotected concrete slabs. The experiments were performed by the Protective Technologies Research & Development Center of the Faculty of Engineering Sciences of the Ben-Gurion University of the Negev (BGU-PTR&DC) under a contract with the Israeli Ministry of Defense (MoD) and the supervision of the IDF Steering Committee for R&D of Protective Structures. The aims of the tests were to: (1) extract data on the dynamic response of an elementary concrete structure to blast loads in order to verify and validate (V&V) our corresponding computer codes; and (2) check the ability of aluminum foams to mitigate blast wave loads. Time-dependent measurements of the response of the concrete slabs to the blast wave loads were successfully recorded using a variety of measurement devices. The obtained data have been used to verify and validate our computer codes.     

No-reference assessment of blur and noise impacts on image quality

The quality of images may be severely degraded in various situations such as imaging during motion, sensing through a diffusive medium, and low signal to noise. Often in such cases, the ideal un-degraded image is not available (no reference exists). This paper overviews past methods that dealt with no-reference (NR) image quality assessment, and then proposes a new NR method for the identification of image distortions and quantification of their impacts on image quality. The proposed method considers both noise and blur distortion types that may exist in the image. The same methodology employed in the spatial frequency domain is used to evaluate both distortion impacts on image quality, while noise power is further independently estimated in the spatial domain. Specific distortions addressed here include additive white noise, Gaussian blur and de-focus blur. Estimation results are compared to the true distortion quantities, over a set of 75 different images.     

Improving the multicommodity flow rates with network codes for two sources

In this work we introduce a construction and analysis of network codes for two sources. The region of achievable rates for this problem is still unknown. The scheme we suggest is based on modifying the multicommodity flow solution and thus improving the achievable rate region, w.r.t the uncoded case. The similarity to the flow problem allows our method to be implemented distributively. We show how the construction algorithm can be combined with distributed backpressure routing algorithms for wireless ad-hoc networks. For both the nondistributed case and the distributed case, the computational complexity of our algorithm for network coding is comparable to that of the parallel multicommodity flow problem. We provide non trivial upper and lower bounds on the performance of our scheme, using random coding techniques.     

Carbon cycling in a zero-discharge mariculture system

Interest in mariculture systems will rise in the near future due to the decreased ability of the ocean to supply the increasing demand for seafood. We present a trace study using stable carbon and nitrogen isotopes and chemical profiles of a zero-discharge mariculture system stocked with the gilthead seabream (Sparus aurata). Water quality maintenance in the system is based on two biofiltration steps. Firstly, an aerobic treatment step comprising a trickling filter in which ammonia is oxidized to nitrate. Secondly, an anaerobic step comprised of a digestion basin and a fluidized bed reactor where excess organic matter and nitrate are removed. Dissolved inorganic carbon and alkalinity values were higher in the anaerobic loop than in the aerobic loop, in agreement with the main biological processes taking place in the two treatment steps. The δ¹³C of the dissolved inorganic carbon (δ¹³C_DIC) was depleted in ¹³C in the anaerobic loop as compared to the aerobic loop by 2.5-3‰. This is in agreement with the higher dissolved inorganic carbon concentrations in the anaerobic loop and the low water retention time and the chemolithotrophic activity of the aerobic loop. The δ¹³C and δ¹⁵N of organic matter in the mariculture system indicated that fish fed solely on feed pellets. Compared to feed pellets and particulate organic matter, the sludge in the digestion basin was enriched in ¹⁵N while δ¹³C was not significantly different. This latter finding points to an intensive microbial degradation of the organic matter taking place in the anaerobic treatment step of the system.