Settling behaviour of thin curved particles in quiescent fluid and turbulence

The motion of thin curved falling particles is ubiquitous in both nature and industry but is not yet widely examined. Here, we describe an experimental study on the dynamics of thin cylindrical shells resembling broken bottle fragments settling through quiescent fluid and homogeneous anisotropic turbulence. The particles have Archimedes numbers based on the mean descent velocity $0.75 \times 10^4 \lesssim Ar \lesssim 2.75 \times 10^4$. Turbulence reaching a Reynolds number of $Re_\lambda \approx 100$ is generated in a water tank using random jet arrays mounted in a co-planar configuration. After the flow becomes statistically stationary, a particle is released and its three-dimensional motion is recorded using two orthogonally positioned high-speed cameras. We propose a simple pendulum model that accurately captures the velocity fluctuations of the particles in still fluid and find that differences in the falling style might be explained by a better alignment of the particle incidence angle with its velocity direction. By comparing the trajectories under background turbulence with the quiescent fluid cases, we measure a decrease in the mean descent velocity in turbulence for the conditions tested. We also study the secondary motion of the particles and identify descent events that are unique to turbulence such as 'long gliding' and 'rapid rotation' events. Lastly, we show an increase in the radial dispersion of the particles under background turbulence and correlate the timescale of descent events with the local settling velocity.Comment: 25 pages, 18 figures, 5 movie

An Analysis of the Blockcipher-Based Hash Functions from PGV

Preneel, Govaerts, and Vandewalle (1993) considered the 64 most basic ways to construct a hash function H: {0, 1}*->{0, 1}(n) from a blockcipher E: {0, 1}(n) x {0, 1}(n)->{0,1}(n). They regarded 12 of these 64 schemes as secure, though no proofs or formal claims were given. Here we provide a proof-based treatment of the PGV schemes. We show that, in the ideal-cipher model, the 12 schemes considered secure by PGV really are secure: we give tight upper and lower bounds on their collision resistance. Furthermore, by stepping outside of the Merkle-Damgard approach to analysis, we show that an additional 8 of the PGV schemes are just as collision resistant (up to a constant). Nonetheless, we are able to differentiate among the 20 collision-resistant schemes by considering their preimage resistance: only the 12 initial schemes enjoy optimal preimage resistance. Our work demonstrates that proving ideal-cipher-model bounds is a feasible and useful step for understanding the security of blockcipher-based hash-function constructions

Facial Reconstruction: Anthropometric Studies Regarding the Morphology of the Nose for Romanian Adult Population I: Nose Width

Craniofacial reconstruction often represents a final step in medico-legal identification and is dependent on facial tissue thickness measurements and feature shape estimation. This study’s aim is to create a reliable and readily reproductible method of predicting the maximum nose width (MNW) based on the maximum nasal aperture width (MAW) for a Romanian adult population. A sample of 55 computer tomography (CT) scans consisting of Romanian adult subjects was selected from the database of a neurosurgery hospital. The craniometrics measured consisted of a first measure of MAW and second one of the MNW using 3D systems Freeform Modelling Plus Software. Correlation analysis indicated a moderate link between the MAW and the MNW. Regression analysis showed that MAW and sex form a statistically significant regression pattern (R2 = 0.340, SEE (Standard Error of Estimate) = 3.801). The preliminary results obtained provide reliable predictions of MNW for facial reconstruction based on MAW measured on the skull

Cohort study of Western Australia computed tomography utilisation patterns and their policy implications

Background: Computed tomography (CT) scanning is a relatively high radiation dose diagnostic imaging modality with increasing concerns about radiation exposure burden at the population level in scientific literature. This study examined the epidemiology of adult CT utilisation in Western Australia (WA) in both the public hospital and private practice settings, and the policy implications. Methods: Retrospective cohort design using aggregate adult CT data from WA public hospitals and Medical Benefits Schedule (MBS) (mid-2006 to mid-2012). CT scanning trends by sex, age, provider setting and anatomical areas were explored using crude CT scanning rates, age-standardised CT scanning rates and Poisson regression modelling. Results: From mid-2006 to mid-2012 the WA adult CT scanning rate was 129 scans per 1,000 person-years (PY). Females were consistently scanned at a higher rate than males. Patients over 65 years presented the highest scanning rates (over 300 scans per 1,000 PY). Private practice accounted for 73% of adult CT scans, comprising the majority in every anatomical area. In the private setting females predominately held higher age-standardised CT scanning rates than males. This trend reversed in the public hospital setting. Patients over 85 years in the public hospital setting were the most likely age group CT scanned in nine of ten anatomical areas. Patients in the private practice setting aged 85+ years were relatively less prominent across every anatomical area, and the least likely age group scanned in facial bones and multiple areas CT scans.Conclusion: In comparison to the public hospital setting, the MBS subsidised private sector tended to service females and relatively younger patients with a more diverse range of anatomical areas, constituting the majority of CT scans performed in WA. Patient risk and subsequent burden is greater for females, lower ages and some anatomical areas. In the context of a national health system, Australia has various avenues to monitor radiation exposure levels, improve physician training and modify funding mechanisms to ensure individual and population medical radiation exposure is as low as reasonably achievable

Security Analysis of NIST CTR-DRBG

We study the security of CTR-DRBG, one of NIST\u27s recommended Pseudorandom Number Generator (PRNG) designs. Recently, Woodage and Shumow (Eurocrypt\u27 19), and then Cohney et al. (S&P\u27 20) point out some potential vulnerabilities in both NIST specification and common implementations of CTR-DRBG. While these researchers do suggest counter-measures, the security of the patched CTR-DRBG is still questionable. Our work fills this gap, proving that CTR-DRBG satisfies the robustness notion of Dodis et al. (CCS\u2713), the standard security goal for PRNGs

Security in the Presence of Key Reuse: Context-Separable Interfaces and their Applications

Key separation is often difficult to enforce in practice. While key reuse can be catastrophic for security, we know of a number of cryptographic schemes for which it is provably safe. But existing formal models, such as the notions of joint security (Haber-Pinkas, CCS ’01) and agility (Acar et al., EUROCRYPT ’10), do not address the full range of key-reuse attacks—in particular, those that break the abstraction of the scheme, or exploit protocol interactions at a higher level of abstraction. This work attends to these vectors by focusing on two key elements: the game that codifies the scheme under attack, as well as its intended adversarial model; and the underlying interface that exposes secret key operations for use by the game. Our main security experiment considers the implications of using an interface (in practice, the API of a software library or a hardware platform such as TPM) to realize the scheme specified by the game when the interface is shared with other unspecified, insecure, or even malicious applications. After building up a definitional framework, we apply it to the analysis of two real-world schemes: the EdDSA signature algorithm and the Noise protocol framework. Both provide some degree of context separability, a design pattern for interfaces and their applications that aids in the deployment of secure protocols