Hardware Security in the Dark

The increasing transistor count on a single chip provides an unprecedented amount of resources for chip designers. Unfortunately, the power consumed by each transistor does not shrink similarly, decreasing the amount of transistors that can be on simultaneously. This utilization wall leaves a growing percentage of transistors dark, or powered-off, as the chip cannot (a) provide the necessary current or (b) maintain a low operating temperature. To account for dark silicon, the computer architecture community has begun taking advantage of the wealth of available transistors to design efficient, time-sharing systems, often through specialized architectures. Meanwhile, security is quickly becoming a first-tier design constraint, increasing the need for hardware security mechanisms, in order to maintain high levels of availability and to detect and protect from intrusion. As we move into the many-core environment, many of these security mechanisms will need to be integrated on-chip. In a chip-multiprocessor environment, security will be necessary as multiple programs or users are sharing resources, thus facilitating attacks. In both a single-user and multiple-user environment, designers can build specialized hardware to provide support for security functions, such as authenticity, cryptography, and intrusion detection. In this paper, we survey current hardware security trends and provide insight on how future chip designs can leverage dark silicon for more secure designs. We provide preliminary designs and discuss future challenges and opportunities in dark silicon security. The merging of hardware security and dark silicon will facilitate efficient, fast, and secure designs.     

Chemical and Structural Widths of Interfaces and Grain Boundaries in Silicon Nitride–Silicon Carbide Whisker Composites

The extent of chemical distributions into crystals bounding whisker/matrix interfaces and matrix grain boundaries and the lateral continuity of the distributions was investigated by analytical electron microscopy methods and compared to their structural widths determined by high-resolution TEM. The extent of the distributions into the bounding crystals, defined as chemical widths, was 10 to 120 times the structural widths; this ratio was larger for grain boundaries than for the interfaces. Further, the chemical distributions were laterally discontinuous at interfaces but continuous at grain boundaries. The elements from the sintering aids, Y₂O₃ and Al₂O₃, were the primary chemical distribution constituents. The distributions were examined by the new position-resolved electron energy loss spectroscopy and Z-contrast scanning TEM methods. Microstructural observations indicated that chemical widths resulted from solid-state diffusion into the bounding crystals and that lateral discontinuities in the distributions resulted from preferential Gibbs–Thompson solution effects of the whisker surfaces at interfaces. These nonequilibrium distributions are process-dependent, and are expected to affect composite properties.     

Artificial neural networks for modelling the mechanical properties of steels in various applications

The application of artificial neural networks (ANNs) in predicting some key properties of steels is discussed in detail. This paper reports on the effectiveness of three back-propagation artificial neural network models that predict (i) the impact toughness of quenched and tempered pressure vessel steel exposed to multiple postweld heat treatment (PWHT) cycles, (ii) the hardness of the simulated heat affected zone in pipeline and tap fitting steels after in-service welding and (iii) the hot ductility and hot strength of various microalloyed steels over the temperature range for strand or slab straightening in the continuous casting process. Predicted and actual experimental values for each model are well matched and highlight the success of applying ANNs in predicting mechanical properties. The capability of ANNs in predicting multiple outputs (hot ductility and hot strength) is also demonstrated.

The sensitivity, which is a measure of the response of an output across the range of an individual input variable, of key input variables (individual alloys and/or process steps) for each model is shown to be in agreement with findings of both the experimental investigation and reports in the literature. Although this paper shows that ANNs can be employed for optimizing steel and process design parameters, some difficulty can arise when inter-relationships exist between input variables. An understanding of the inter-relationships between input variables is essential for interpreting the sensitivity data and optimizing design parameters. It is argued that artificial neural network models can be developed that have the capacity to eliminate the need for expensive experimental investigation in areas, such as welding (new and repair), inspection and testing, and manufacturing processes.     

A replica technique for extracting precipitates from zirconium alloys for transmission electron microscopy analysis

A reliable two-stage carbon replica technique has been developed to extract precipitates from zirconium alloys. Using this technique, all precipitating phases can be extracted from Zircaloy-2, Zr-Cr-Fe, and Zr-Nb-Fe alloys. Precipitate identification using EDS X-ray analysis and convergent beam electron diffraction was greatly facilitated in comparison to thin foils. In addition, the sensitivity for the detection of trace elements in particles was increased using extraction replicas. The chemical compositions of the precipitates as determined from both replica and thin foils were in excellent agreement.     

PCR-based gene synthesis as an efficient approach for expression of the A+T-rich malaria genome

The A+T-rich genome of the human malaria parasite Plasmodiumfalciparum encodes genes of biological importance that cannotbe expressed efficiently in heterologous eukaryotic systems,owing to an extremely biased codon usage and the presence ofnumerous cryptic polyadenylation sites. In this work we haveoptimized an assembly polymerase chain reaction (PCR) methodfor the fast and extremely accurate synthesis of a 2.1 kb Plasmodiumfalciparum gene (pfsub-1) encoding a subtilisin-like protease.A total of 104 oligonucleotides, designed with the aid of dedicatedcomputer software, were assembled in a single-step PCR. Theassembly was then further amplified by PCR to produce a syntheticgene which has been cloned and successfully expressed in bothPichia pastoris and recombinant baculovirus-infected High Five^TMcells. We believe this strategy to be of special interest asit is simple, accessible and has no limitation with respectto the size of the gene to be synthesized. Used as a systematicapproach for the malarial genome or any other A + T-rich organism,the method allows the rapid synthesis of a nucleotide sequenceoptimized for expression in the system of choice and productionof sufficiently large amounts of biological material for completemolecular and structural characterization.     

Infants communicate in order to be understood.

Infants intentionally communicate with others from before their 1st birthday. But there is some question about how they understand the communicative process. Do they understand that for their request to work the recipient must both understand the request and be cooperatively disposed to fulfill it? On the basis of the study by Shwe and Markman (1997), we developed a new paradigm that tested whether and how 18-, 24-, and 30-month-old children repair a failed request. Children at all ages repaired their requests in the case of a misunderstanding even if they had obtained the requested object already. They also repaired differently depending on the precise reason for the communicative failure (e.g., misunderstanding the referent versus the communicative intent) and did not repair in the case of correct understanding, even if they did not get the requested object. Thus, from very early in their communicative careers, young children operate with a basic understanding of the mental and cooperative nature of human communication. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of rumen microbial populations in lactating dairy cattle fed diets varying in carbohydrate profiles and Saccharomyces cerevisiae fermentation product

The rumen microbial ecosystem is a critical factor that links diets to bovine physiology and productivity; however, information about dietary effects on microbial populations has generally been limited to small numbers of samples and qualitative assessment. To assess whether consistent shifts in microbial populations occur in response to common dietary manipulations in dairy cattle, samples of rumen contents were collected from 2 studies for analysis by quantitative real-time PCR (qPCR). In one study, lactating Holstein cows (n = 8) were fed diets in which a nonforage fiber source replaced an increasing proportion of forages and concentrates in a 4 × 4 Latin square design, and samples of ruminal digesta were collected at 9-h intervals over 3 d at the end of each period. In the second study, lactating Holstein cows (n = 15) were fed diets with or without the inclusion of a Saccharomyces cerevisiae fermentation product (SCFP) in a crossover design. In this study, rumen liquid and solid samples were collected during total rumen evacuations before and after feeding in a 42-h period. In total, 146 samples of ruminal digesta were used for microbial DNA isolation and analysis by qPCR. Validated primer sets were used to quantify total bacterial and anaerobic fungal populations as well as 12 well-studied bacterial taxa. The relative abundance of the target populations was similar to those previously reported. No significant treatment effects were observed for any target population. A significant interaction of treatment and dry matter intake was observed, however, for the abundance of Eubacterium ruminantium. Increasing dry matter intake was associated with a quadratic decrease in E. ruminantium populations in control animals but with a quadratic increase in E.ruminantium populations in cows fed SCFP. Analysis of sample time effects revealed that Fibrobacter succinogenes and fungal populations were more abundant postfeeding, whereas Ruminococcus albus tended to be more abundant prefeeding. Seven of the target taxa were more abundant in either the liquid or solid fractions of ruminal digesta. By accounting for the total mass of liquid and solid fractions in the rumen and the relative abundance of total bacteria in each fraction, it was estimated that 92% of total bacteria were found in the solid digesta fraction.     

Effect of synthesis variables on the fluorescence properties of CdSe-polystyrene latexes

The development of photoluminescent materials based on the incorporation of quantum dots (QDs) into polymeric latexes has gained importance due to the multiple potential applications. Through the process of miniemulsion polymerization it is possible to encapsulate quantum particles into polymer matrix to provide both chemical stability and to maintain emission properties. The polymerization process was achieved with continuous magnetic stirring and nitrogen atmosphere. Cetyl trimethylammonium bromide (CTAB) was used as surfactant at concentration levels of 1.3 × 10^-3, 3.2 × 10^-3 and 5.4 × 10^-3 M. The initiator 2,2-azobisisobutyronitrile (AIBN) was used at 0.50 and 0.75 wt% and CdSe QDS were used at 0.075, 0.15 and 0.225 wt%, both in relation to monomer content. A STEM study on the composite latexes and later a statistical study on the measurement of polymer particle diameter let us corroborate that the increment in surfactant concentration produces a decrement in polymer particle size. The obtained composite latexes were stable and showed fluorescence by excitation with UV light. The spectrofluorometry studies indicated that in composite latexes fluorescent emission was a function of polymer particle size, showing higher intensity those formulations with smaller surfactant concentrations and bigger polymer particle size.     

Interfacially Driven Deformation Twinning in Bulk Ag-Cu Composites

Interfaces and interface/defect interactions increasingly dominate the mechanical response of materials as the dimensions of the grains decrease to the nanoscale. Recently, we reported unusually profuse deformation twinning in Ag-Cu layered eutectic composites with bilayer thicknesses in the submicron regime (~200?nm?C400?nm) at room temperature and low strain rates. Using atomistic simulations and dislocation theory, we propose that the Ag-Cu interface facilitated deformation twinning in Cu by permitting the transmission of twinning partials from Ag to Cu. In this way, twins in Ag can provide an ample supply of twinning partials to Cu to support and sustain twin growth in Cu during deformation. Interface-driven twinning as revealed by this study suggests the exciting possibility of altering the roles of dislocation slip and twinning through the design of heterophase interface structure and properties.