Columnar structure formation of a dilute suspension of settling spherical particles in a quiescent fluid

The settling of heavy spherical particles in a column of quiescent fluid is investigated. The performed experiments cover a range of Galileo numbers ($110 \leq \text{Ga} \leq 310$) for a fixed density ratio of $\Gamma = \rho_p/\rho_f = 2.5$. In this regime the particles are known (M. Jenny, J. Du\v{s}ek and G. Bouchet, Journal of Fluid Mechanics 508, 201 (2004).) to show a variety of motions. It is known that the wake undergoes several transitions for increasing $\text{Ga}$ resulting in particle motions that are successively: vertical, oblique, oblique oscillating, and finally chaotic. Not only does this change the trajectory of single, isolated, settling particles, but it also changes the dynamics of a swarm of particles as collective effects become important even for dilute suspensions, with volume fraction up to $\Phi_V = \mathcal{O}\left(10^{-3}\right)$, which are investigated in this work. Multi-camera recordings of settling particles are recorded and tracked over time in 3 dimensions. A variety of analysis are performed and show a strong clustering behavior. The distribution of the cell areas of the Vorono\"i tessellation in the horizontal plane are compared to that of a random distribution of particles and shows clear clustering. Moreover, a negative correlation was found between the Vorono\"i area and the particle velocity; clustered particles fall faster. In addition, the angle between two adjacent particles and the vertical is calculated and compared to a homogeneous distribution of particles, clear evidence of vertical alignment of particles is found. The experimental findings are compared to simulations.Comment: 8 pages, 6 figure

System-level Non-interference for Constant-time Cryptography

International audienceCache-based attacks are a class of side-channel attacks that are particularly effective in virtualized or cloud-based en-vironments, where they have been used to recover secret keys from cryptographic implementations. One common ap-proach to thwart cache-based attacks is to use constant-time implementations, i.e. which do not branch on secrets and do not perform memory accesses that depend on secrets. How-ever, there is no rigorous proof that constant-time implemen-tations are protected against concurrent cache-attacks in virtualization platforms with shared cache; moreover, many prominent implementations are not constant-time. An alter-native approach is to rely on system-level mechanisms. One recent such mechanism is stealth memory, which provisions a small amount of private cache for programs to carry po-tentially leaking computations securely. Stealth memory in-duces a weak form of constant-time, called S-constant-time, which encompasses some widely used cryptographic imple-mentations. However, there is no rigorous analysis of stealth memory and S-constant-time, and no tool support for check-ing if applications are S-constant-time. We propose a new information-flow analysis that checks if an x86 application executes in constant-time, or in S-constant-time. Moreover, we prove that constant-time (resp. S-constant-time) programs do not leak confidential infor-mation through the cache to other operating systems exe-cuting concurrently on virtualization platforms (resp. plat-forms supporting stealth memory). The soundness proofs are based on new theorems of independent interest, includ-ing isolation theorems for virtualization platforms (resp. plat-forms supporting stealth memory), and proofs that constant-time implementations (resp. S-constant-time implementa-tions) are non-interfering with respect to a strict information flow policy which disallows that control flow and memory ac-cesses depend on secrets. We formalize our results using the Coq proof assistant and we demonstrate the effectiveness of our analyses on cryptographic implementations, including PolarSSL AES, DES and RC4, SHA256 and Salsa20

Output-sensitive Information flow analysis

Part 1: Full PapersInternational audienceConstant-time programming is a countermeasure to prevent cache based attacks where programs should not perform memory accesses that depend on secrets. In some cases this policy can be safely relaxed if one can prove that the program does not leak more information than the public outputs of the computation. We propose a novel approach for verifying constant-time programming based on a new information flow property, called output-sensitive non-interference. Noninterference states that a public observer cannot learn anything about the private data. Since real systems need to intentionally declassify some information, this property is too strong in practice. In order to take into account public outputs we proceed as follows: instead of using complex explicit declassification policies, we partition variables in three sets: input, output and leakage variables. Then, we propose a typing system to statically check that leakage variables do not leak more information about the secret inputs than the public normal output. The novelty of our approach is that we track the dependence of leakage variables with respect not only to the initial values of input variables (as in classical approaches for noninterference), but taking also into account the final values of output variables. We adapted this approach to LLVM IR and we developed a prototype to verify LLVM implementations

Validation of Abstract Side-Channel Models for Computer Architectures

Observational models make tractable the analysis of information flow properties by providing an abstraction of side channels. We introduce a methodology and a tool, Scam-V, to validate observational models for modern computer architectures. We combine symbolic execution, relational analysis, and different program generation techniques to generate experiments and validate the models. An experiment consists of a randomly generated program together with two inputs that are observationally equivalent according to the model under the test. Validation is done by checking indistinguishability of the two inputs on real hardware by executing the program and analyzing the side channel. We have evaluated our framework by validating models that abstract the data-cache side channel of a Raspberry Pi 3 board with a processor implementing the ARMv8-A architecture. Our results show that Scam-V can identify bugs in the implementation of the models and generate test programs which invalidate the models due to hidden microarchitectural behavior

Agricultural Academy

abstract DoycheV, V. and G. MihayloVa, 2013. Effect of flaxseed and alpha tocopherol supplementation of pig diets on fatty acid content and lipid oxidation stability of m. Longissimus. Bulg. J. Agric. Sci., 19: 1416-1424 The experiment was carried out with 70 fattening hybrid pigs (45-110 kg) divided into 5 groups of 14 (7 castrated males and 7 females). Pigs were fed compound feed containing 13.24% CP and 12.04 MJ ME/кg. During the last two months of the fattening period (78-120 kg) the compound feed of pigs from groups ІІ, ІІІ, ІV and V (experimental) was supplemented with flaxseed at different levels: group II -4%, group III -8%; groups IV and V -12%. The feed of pigs from group V was also supplemented with vitamin E (alpha tocopherol acetate) at 200 mg/kg. Pigs were slaughtered at 120 kg live body weight. The fatty acid contents of triacylglycerols and phospholipids were determined in m. Longissimus samples. Oxidative changes in m. Longissimus meat were assessed in fresh samples and in samples stored at -18°С for 6 months. Linolenic acid content of triacylglycerols increased in experimental groups, being statistically significant higher in group II (Р<0.01), III, IV and V (Р<0.001) vs group I. Linoleic acid concentrations also differed between groups II and III (Р<0.05), group II and both groups IV and V (Р<0.001) and groups III and IV (Р<0.01). Compared to control pigs, eicosapentaenoic acid content in tissue triacylglycerols was higher in group III (Р<0.05), IV and V (Р<0.01). Significant differences were also established in groups IV and V vs group II (Р<0.05). Linoleic acid content decreased in group III vs group I (Р<0.05) and group II (Р<0.01), whereas arachidonic acid changed only slightly. The PUFA content was also insignificantly altered. Compared to the non-supplemented group, the PUFA/SFA ratio was substantially higher in groups II, IV and V (Р<0.01) and III (Р<0.05). The n-6/n-3 ratio in groups III, IV and V was significantly lower than that of groups I and II (Р<0.001). The difference between groups I and II was also considerable (Р<0.001). Linolenic acid in tissue phospholipids of group III was significantly more than that in groups I (Р<0.01) and II (Р<0.05). In groups IV and V, the content f this fatty acid was higher than that in groups I, II (Р<0.001) and III (Р<0.01). The eicosapentaenoic acid in groups IV and V was considerably higher than that in control (Р<0.05). There were no statistically significant differences between groups with regard to fatty acid groups. The n-6/n-3 ratio was lower in group II vs group I (Р<0.05) and in groups III, IV and V (Р<0.001) vs group I. The differences between groups IV and V vs group II were also important (Р<0.01). The high content of PUFA in tissue lipids resulted in significantly higher thiobarbituric acid number in both fresh and stored meat