The Frequency Dependence of Critical-velocity Behavior in Oscillatory Flow of Superfluid Helium-4 Through a 2-micrometer by 2-micrometer Aperture in a Thin Foil

The critical-velocity behavior of oscillatory superfluid Helium-4 flow through a 2-micrometer by 2-micrometer aperture in a 0.1-micrometer-thick foil has been studied from 0.36 K to 2.10 K at frequencies from less than 50 Hz up to above 1880 Hz. The pressure remained less than 0.5 bar. In early runs during which the frequency remained below 400 Hz, the critical velocity was a nearly-linearly decreasing function of increasing temperature throughout the region of temperature studied. In runs at the lowest frequencies, isolated 2 Pi phase slips could be observed at the onset of dissipation. In runs with frequencies higher than 400 Hz, downward curvature was observed in the decrease of critical velocity with increasing temperature. In addition, above 500 Hz an alteration in supercritical behavior was seen at the lower temperatures, involving the appearance of large energy-loss events. These irregular events typically lasted a few tens of half-cycles of oscillation and could involve hundreds of times more energy loss than would have occurred in a single complete 2 Pi phase slip at maximum flow. The temperatures at which this altered behavior was observed rose with frequency, from ~ 0.6 K and below, at 500 Hz, to ~ 1.0 K and below, at 1880 Hz.Comment: 35 pages, 13 figures, prequel to cond-mat/050203

The purpose of United Nations Security Council practice: Contesting competence claims in the normative context created by the Responsibility to Protect.

Practice theory provides important insight into the workings of the Security Council. The contribution is currently limited however by the conjecture that practice theory operates on ‘a different analytical plane’ to norm / normative theory (Adler-Nissen and Pouliot 2014). Building on existing critiques (Duval and Chowdhury 2011; Schindler and Wille 2015) we argue that analyzing practices separately from normative positions risks misappropriating competence and reifying practice that is not fit for purpose. This risk is realized in Adler-Nissen and Pouliot’s (2014) practice based account Libya crisis. By returning the normative context created by the Responsibility to Protect (R2P) to the analytical foreground, and by drawing on a pragmatic conception of 'ethical competence' (Frost 2009), we find that pre-reflexive practices uncritically accepted as markers of competence – e.g. ‘penholding’ – can contribute to the Council’s failure to act collectively in the face of mass atrocity. Drawing on extensive interview material we offer an alternative account of the Libya intervention, finding that the practices of the permanent three (France, UK and US) did not cultivate the kind of collective consciousness that is required to implement R2P. This is further illustrated by an account of the Security Council’s failure in Syria, where the P3’s insistence on regime change instrumentalized the Council at the expense of R2P-appropriate practice. This changed when elected members became ‘penholders’. Practice theory can facilitate learning processes that help the Council meet its responsibilities, but only through an approach that combines its insights with those of norm / normative theory

Speeding up Quantified Bit-Vector SMT Solvers by Bit-Width Reductions and Extensions

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Mind the Gap - A Closer Look at the Security of Block Ciphers against Differential Cryptanalysis

Resistance against differential cryptanalysis is an important design criteria for any modern block cipher and most designs rely on finding some upper bound on probability of single differential characteristics. However, already at EUROCRYPT'91, Lai et al. comprehended that differential cryptanalysis rather uses differentials instead of single characteristics. In this paper, we consider exactly the gap between these two approaches and investigate this gap in the context of recent lightweight cryptographic primitives. This shows that for many recent designs like Midori, Skinny or Sparx one has to be careful as bounds from counting the number of active S-boxes only give an inaccurate evaluation of the best differential distinguishers. For several designs we found new differential distinguishers and show how this gap evolves. We found an 8-round differential distinguisher for Skinny-64 with a probability of 2−56.932−56.93, while the best single characteristic only suggests a probability of 2−722−72. Our approach is integrated into publicly available tools and can easily be used when developing new cryptographic primitives. Moreover, as differential cryptanalysis is critically dependent on the distribution over the keys for the probability of differentials, we provide experiments for some of these new differentials found, in order to confirm that our estimates for the probability are correct. While for Skinny-64 the distribution over the keys follows a Poisson distribution, as one would expect, we noticed that Speck-64 follows a bimodal distribution, and the distribution of Midori-64 suggests a large class of weak keys

A Bit-Vector Differential Model for the Modular Addition by a Constant

ARX algorithms are a class of symmetric-key algorithms constructed by Addition, Rotation, and XOR, which achieve the best software performances in low-end microcontrollers. To evaluate the resistance of an ARX cipher against differential cryptanalysis and its variants, the recent automated methods employ constraint satisfaction solvers, such as SMT solvers, to search for optimal characteristics. The main difficulty to formulate this search as a constraint satisfaction problem is obtaining the differential models of the non-linear operations, that is, the constraints describing the differential probability of each non-linear operation of the cipher. While an efficient bit-vector differential model was obtained for the modular addition with two variable inputs, no differential model for the modular addition by a constant has been proposed so far, preventing ARX ciphers including this operation from being evaluated with automated methods. In this paper, we present the first bit-vector differential model for the n-bit modular addition by a constant input. Our model contains O(log2(n)) basic bit-vector constraints and describes the binary logarithm of the differential probability. We also represent an SMT-based automated method to look for differential characteristics of ARX, including constant additions, and we provide an open-source tool ArxPy to find ARX differential characteristics in a fully automated way. To provide some examples, we have searched for related-key differential characteristics of TEA, XTEA, HIGHT, and LEA, obtaining better results than previous works. Our differential model and our automated tool allow cipher designers to select the best constant inputs for modular additions and cryptanalysts to evaluate the resistance of ARX ciphers against differential attacks.acceptedVersio

Adenovirus-mediated TA-p73β gene transfer increases chemosensitivity of human malignant melanomas

Malignant melanoma is the most aggressive form of skin cancer and has proven to be highly resistant to conventional chemotherapy. Intriguingly, the p53 tumor suppressor, a main mediator of chemoresistance in other tumor types, is rarely mutated in melanoma. However, we have previously shown that anti-apoptotic isoforms of p73 (ΔTA-p73), another member of the p53 family, are overexpressed in metastatic melanomas. ΔTA-p73 can oppose the pro-apoptotic functions of p53 and full length p73, and thus it could contribute to melanoma chemoresistance. In this study, we use an efficient adenoviral-based gene transfer approach to introduce a transcriptionally active form of p73 (TA-p73β) in melanoma cells, with the objective of overcoming drug resistance. Interestingly, TA-p73β significantly sensitized 5 out of 7 aggressive melanoma cell lines to the standard therapeutic agents adriamycin and cisplatin. More importantly, TA-p73β displayed a synergistic effect in vivo allowing adriamycin or cisplatin to block melanoma cell growth in mouse xenograft models ( p < 0.05). In summary, our data show that Ad-mediated TA-p73β gene expression can markedly sensitize a subset of melanoma cell lines to adriamycin and cisplatin in vitro and in vivo , suggesting a new chemosensitization strategy for malignant melanomas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44369/1/10495_2006_Article_3407.pd

Beiträge zum 29. Darmstädter Geotechnik-Kolloquium am 7. März 2024

Themenschwerpunkte: 1. Klimawandelfolgen und Nachhaltigkeit 2. Digitalisierung und künstliche Intelligenz 3. Planung und Bemessung von Infrastrukturprojekten 4. Großprojekt