Cryptanalaysis of an EPCC1G2 Standard Compliant Ownership Transfer Scheme

Recently, Chen and Chien have proposed a novel ownership transfer scheme with low implementation costs and conforming to the EPC Class-1 Generation-2 standard. The authors claimed that the proposed scheme is able to resist all attacks, and hence it has better security and performance than its predecessors. However, in this paper we show that the protocol fails short of its security objectives, and it is even less secure than the previously proposed schemes. In fact, we describe several attacks which allow to recover all the secret information stored in the tag. Obviously, once this information is known, tags can be easily traced and impersonated.     

Brazil’s growing production of scientific articles—how are we doing with review articles and other qualitative indicators?

This article identifies scientific fields in Brazil that have been generating new knowledge, their evolution, tendencies and the relationship between scientific production and the National Postgraduate Program (Programa Nacional de Pós-Graduação—PNPG). It works with review articles and assesses: (a) articles published as reviews by international databases; (b) the growth of Brazilian participation in that context; (c) institutional participation; (d) the predominant fields of knowledge; (e) the most productive authors, and (f) periodicals that published the greatest number of review articles by Brazilian authors. The 5,348 review articles published between 2000 and 2009 were made available in 1,309 scientific publications, and the fields that published the most reviews were Pharmacology, Chemistry, Neurosciences, Biochemistry and Molecular Biology, Psychiatry, Neurology, Endocrinology and Internal Medicine. The reviews were produced by 27,096 authors under the auspices of 20 institutions which, together, answer for 95 % of the Brazilian production, and are public, excepting for the Pontifícia Universidade Católica do Rio Grande do Sul (PUC-RS). In the international scenario, we find that 31 countries are responsible for 90.11 % of the total scientific production and 94.08 % of the review articles. To establish a comparison between Brazil and its closest competitors, these countries can be classified arbitrarily in three groups: (1) countries with a large number of review articles (>3100), an average number of citations above 18, and an h-index greater than 95; (2) countries with a significant production of articles (between 2,000 and 3,000), average number of citations between 12 and 17, and an h-index below 95. Brazil is in the third group, (3) formed by countries with a lower level of production and the two qualitative indicators at opposite poles: the average of citations on a par with the first group (>18) and h-indexes like those of the second group (<95).     

On the contact detection for contact-impact analysis in multibody systems

One of the most important and complex parts of the simulation of multibody systems with contact-impact involves the detection of the precise instant of impact. In general, the periods of contact are very small and, therefore, the selection of the time step for the integration of the time derivatives of the state variables plays a crucial role in the dynamics of multibody systems. The conservative approach is to use very small time steps throughout the analysis. However, this solution is not efficient from the computational view point. When variable time-step integration algorithms are used and the preimpact dynamics does not involve high-frequencies, the integration algorithms may use larger time steps and the contact between two surfaces may start with initial penetrations that are artificially high. This fact leads either to a stall of the integration algorithm or to contact forces that are physically impossible which, in turn, lead to post-impact dynamics that is unrelated to the physical problem. The main purpose of this work is to present a general and comprehensive approach to automatically adjust the time step, in variable time-step integration algorithms, in the vicinity of contact of multibody systems. The proposed methodology ensures that for any impact in a multibody system the time step of the integration is such that any initial penetration is below any prescribed threshold. In the case of the start of contact, and after a time step is complete, the numerical error control of the selected integration algorithm is forced to handle the physical criteria to accept/reject time steps in equal terms with the numerical error control that it normally uses. The main features of this approach are the simplicity of its computational implementation, its good computational efficiency, and its ability to deal with the transitions between non-contact and contact situations in multibody dynamics. A demonstration case provides the results that support the discussion and show the validity of the proposed methodology.     

Improvement of dynamic response in an impact absorber by frictional elements

A novel device that uses friction between one or more pairs of elastic conical rings to dissipate the energy from an impacting body is presented. The device consists of one moving and one stationary cylinders coupled to each other using two pairs of conical rings and a spring. The spring is used to restore the system to its original configuration after the impact. The dynamic response of the system to the impact forces during impact events is analysed numerically and experimentally. The effects of several governing parameters, such as the mass ratio between the cylinders, the duration of the transient response of the device, the magnitude of the rest zone of the moving element and the peak impact force are investigated. The proposed system is applicable in sequential impact scenarios, in which remarkable improvements were observed over traditional solid-rod impact absorbers. The present study may serve as a guide for the design of improved damping devices for impact applications.     

Molecular,rheological, and thermal study of long‐chain branched polypropylene obtained by esterification of anhydride grafted polypropylene

Long‐chain branched polypropylene was prepared using reaction in the molten state in the presence of glycerol and a linear polypropylene functionalized with maleic anhydride (PPg). The concentration of glycerol in the melt was varied in the range from 0.1 to 5 wt % to obtain different levels of branching. FTIR spectroscopy results indicate that the OH groups of glycerol react with the anhydrides on the PPg chains giving place to ester groups. The presence of long‐chain branches in the molecular structure of PPg was confirmed using multiple‐detection size‐exclusion chromatography and rheology. These techniques demonstrate that the level of branching increases with glycerol concentration and that the modification of PPg produces materials with a bimodal distribution of polymer species. Moreover, some of the highly modified materials display gel‐like behavior. The materials also display thermo‐rheological complexity and enhanced activation energy at low frequencies. The crystallization study shows that both the anhydride groups in PPg and the LCBs have opposite nucleating effects. PPg presents the largest activation energy of crystallization and its value decreases with the concentration of glycerol for a given level of crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40357.     

Electrospinning polycaprolactone dissolved in glacial acetic acid: Fiber production,nonwoven characterization,and In Vitro evaluation

The electrospinning of polycaprolactone (PCL) dissolved in glacial acetic acid and the characterization of the resultant nonwoven fiber mats is reported in this work. For comparison purposes, PCL fiber mats were also obtained by electrospinning the polymer dissolved in chloroform. Given the processing parameters chosen, results show that 14 and 17 wt % PCL solutions are not viscous enough and yield beaded fibers, 20 and 23 wt % solutions give rise to high quality fibers and 26 wt % solutions yield mostly irregular and fused fibers. The nonwoven mats are highly porous, retain the high tensile strain of PCL, and the fibers are semicrystalline. Cells adhere and proliferate equally well on all mats, irrespective of the solvent used in their production. In conclusion, mats obtained by electrospinning PCL dissolved in acetic acid are also a good option to consider when producing scaffolds for tissue engineering. Moreover, acetic acid is miscible with polar solvents, which may allow easier blending of PCL with hydrophilic polymers and therefore achieve the production of electrospun nanofibers with improved properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41068.     

Poly(ester amide)s based on l-lactic acid oligomers and glycine: the role of the central unit of the l-lactic acid oligomers and their molecular weight in the poly(ester amide)s properties

Novel biodegradable poly(ester amide)s (PEAs) based on l-lactic acid (l-LA) oligomers and glycine were successfully synthesized, through an easy and fast procedure, making use of inexpensive starting materials. The l-LA oligomers were prepared with different central units and different molecular weights in order to access the influence of such parameters in the final properties of the PEAs’. Both the central unit of the l-LA oligomer and its molecular weight have important influence in the PEAs’ final properties. The thermal stability is lower for the PEAs containing the l-LA with the shortest central unit and for the PEAs based on the l-LA oligomers of high molecular weight. The PEAs exhibit a semi-crystalline nature, except those derived from the l-LA oligomers with high molecular weight, which have an amorphous character. Both hydrolytic and enzymatic degradation are more pronounced in PEAs synthesized from the l-LA oligomers with low molecular weight. Different mechanisms of degradation were found for the PEAs: bulk erosion and surface erosion, for hydrolytic degradation and enzymatic degradation tests, respectively.