Creep of ice: Further studies

Detailed studies have been done of ice creep as related to the icy satellites, Ganymede and Callisto. Included were: (1) the flow of high-pressure water ices II, III, and V, and (2) frictional sliding of ice I sub h. Work was also begun on the study of the effects of impurities on the flow of ice. Test results are summarized

The effect of ring distortions on buckling of blunt conical shells

A rigorous analytical study of cones stiffened by many thin-gage, open-section rings is presented. The results are compared with data previously obtained from uniform pressure tests of the Viking mission flight aeroshell and of the Viking structural prototype aeroshells. A conventional analysis, in which the rings are modeled as discrete rigid cross sections, is shown to lead to large, unconservative strength predictions. A more sophisticated technique of modeling the rings as shell branches leads to much more realistic strength predictions and more accurately predicts the failure modes. It is also shown that if a small initial imperfection proportional to the shape of the buckling mode is assumed, the critical buckling modes from analysis and test are in agreement. However, the reduction in buckling strength from the perfect-shell predictions is small

Stomatopod Crustaceans from the Carolinas and Georgia, Southeastern United States

Literature and specimen records are updated for stomatopod crustaceans known from the coasts of the Carolinas and Georgia. Gibbesia, new genus, is recognized for Squilla neglecta, and a new species, Neogonodactylus wennerae, is named for an offshore species of Neogonodactylus previously identified with the Caribbean shore species N. bredini. Fifteen species of stomatopods representing 12 genera are now known from the area: Bigelowina biminiensis (Bigelow), Cloridopsis dubia (Milne Edwards), Coronis scolopendra Latreille, Gibbesia neglecta (Gibbes), Heterosquilloides armata (Smith), Meiosquilla quadridens (Bigelow), Lysiosquilla scabricauda (Lamarck), Lysiosquillina glabriuscula (Lamarck), Nannosquilla carolinensis Manning, N. whitingi Camp & Manning, Neogonodactylus torus (Manning), Neogonodactylus wennerae, new species, Platysquilloides enodis (Manning), Squilla deceptrix Manning, and S. empusa Say. A key is provided to species known from the Carolinas and Georgia

Keyed Non-Parametric Hypothesis Tests

The recent popularity of machine learning calls for a deeper understanding of AI security. Amongst the numerous AI threats published so far, poisoning attacks currently attract considerable attention. In a poisoning attack the opponent partially tampers the dataset used for learning to mislead the classifier during the testing phase. This paper proposes a new protection strategy against poisoning attacks. The technique relies on a new primitive called keyed non-parametric hypothesis tests allowing to evaluate under adversarial conditions the training input's conformance with a previously learned distribution $\mathfrak{D}$. To do so we use a secret key $\kappa$ unknown to the opponent. Keyed non-parametric hypothesis tests differs from classical tests in that the secrecy of $\kappa$ prevents the opponent from misleading the keyed test into concluding that a (significantly) tampered dataset belongs to $\mathfrak{D}$.Comment: Paper published in NSS 201

Langevin Thermostat for Rigid Body Dynamics

We present a new method for isothermal rigid body simulations using the quaternion representation and Langevin dynamics. It can be combined with the traditional Langevin or gradient (Brownian) dynamics for the translational degrees of freedom to correctly sample the NVT distribution in a simulation of rigid molecules. We propose simple, quasi-symplectic second-order numerical integrators and test their performance on the TIP4P model of water. We also investigate the optimal choice of thermostat parameters.Comment: 15 pages, 13 figures, 1 tabl

Grafius and Anderson

It is widely assumed that, among detritivorous stream invertebrates, shredders facilitate collectors through their role in producing particles from coarser detritus. While this hypothesis is plausible, we argue that it has not been adequately tested. It has not even been clear what information would be necessary or sufficient to document such an interaction. We outline the evidence which we believe must be sought: it must be established that collectors are particle-limited, that shredder activity produces particles, that shredder activity enhances collector performance, and that the mechanism for this enhancement lies in particle production and not some other process. We review available data that bear on these propositions, and describe a straightforward experiment which could unambiguously test the shredder-collector facilitation hypothesis. Invertebrate faunas of forest streams are often dominated by detritivores which feed on organic matter derived largely from leaf litter. Two major functional groups can be distinguished among them: shredders, which consume coarse particulate organic matter (CPOM), and collectors, which consume fine particles (FPOM) filtered from the water column or gathered from sediments. Shredders process CPOM and produce particles as they feed, and it is widely believed that shredders facilitate collectors as a result of this particle production (e.g. These putative shredder-collector interactions are important for at least three reasons. First, on a local scale, effects of shredders on collector performance have obvious consequences for productivity throughout stream food webs. These effects are likely to have ecological and economic implications beyond the stream itself. For instance, increased collector growth should allow greater productivity of stream fish, which in turn will benefit terrestrial piscivores and commercial and sports fisheries. In addition, the emergent adults of stream collectors can be a major resource for terrestrial and aerial insectivores, and some are also important pests -for instance, black flies. Second, on a much larger spatial scale, shredder-collector facilitation (at the level of whole functional groups) is a major element of the River Continuum Concep

Space tug propulsion system failure mode, effects and criticality analysis

For purposes of the study, the propulsion system was considered as consisting of the following: (1) main engine system, (2) auxiliary propulsion system, (3) pneumatic system, (4) hydrogen feed, fill, drain and vent system, (5) oxygen feed, fill, drain and vent system, and (6) helium reentry purge system. Each component was critically examined to identify possible failure modes and the subsequent effect on mission success. Each space tug mission consists of three phases: launch to separation from shuttle, separation to redocking, and redocking to landing. The analysis considered the results of failure of a component during each phase of the mission. After the failure modes of each component were tabulated, those components whose failure would result in possible or certain loss of mission or inability to return the Tug to ground were identified as critical components and a criticality number determined for each. The criticality number of a component denotes the number of mission failures in one million missions due to the loss of that component. A total of 68 components were identified as critical with criticality numbers ranging from 1 to 2990

New Langevin and Gradient Thermostats for Rigid Body Dynamics

We introduce two new thermostats, one of Langevin type and one of gradient (Brownian) type, for rigid body dynamics. We formulate rotation using the quaternion representation of angular coordinates; both thermostats preserve the unit length of quaternions. The Langevin thermostat also ensures that the conjugate angular momenta stay within the tangent space of the quaternion coordinates, as required by the Hamiltonian dynamics of rigid bodies. We have constructed three geometric numerical integrators for the Langevin thermostat and one for the gradient thermostat. The numerical integrators reflect key properties of the thermostats themselves. Namely, they all preserve the unit length of quaternions, automatically, without the need of a projection onto the unit sphere. The Langevin integrators also ensure that the angular momenta remain within the tangent space of the quaternion coordinates. The Langevin integrators are quasi-symplectic and of weak order two. The numerical method for the gradient thermostat is of weak order one. Its construction exploits ideas of Lie-group type integrators for differential equations on manifolds. We numerically compare the discretization errors of the Langevin integrators, as well as the efficiency of the gradient integrator compared to the Langevin ones when used in the simulation of rigid TIP4P water model with smoothly truncated electrostatic interactions. We observe that the gradient integrator is computationally less efficient than the Langevin integrators. We also compare the relative accuracy of the Langevin integrators in evaluating various static quantities and give recommendations as to the choice of an appropriate integrator.Comment: 16 pages, 4 figure

Characterisation and improvement of j(O¹D) filter radiometers

Atmospheric O3 → O(1D) photolysis frequencies j(O1D) are crucial parameters for atmospheric photochemistry because of their importance for primary OH formation. Filter radiometers have been used for many years for in situ field measurements of j(O1D). Typically the relationship between the output of the instruments and j(O1D) is non-linear because of changes in the shape of the solar spectrum dependent on solar zenith angles and total ozone columns. These non-linearities can be compensated for by a correction method based on laboratory measurements of the spectral sensitivity of the filter radiometer and simulated solar actinic flux density spectra. Although this correction is routinely applied, the results of a previous field comparison study of several filter radiometers revealed that some corrections were inadequate. In this work the spectral characterisations of seven instruments were revised, and the correction procedures were updated and harmonised considering recent recommendations of absorption cross sections and quantum yields of the photolysis process O3 → O(1D). Previous inconsistencies were largely removed using these procedures. In addition, optical interference filters were replaced to improve the spectral properties of the instruments. Successive determinations of spectral sensitivities and field comparisons of the modified instruments with a spectroradiometer reference confirmed the improved performance. Overall, filter radiometers remain a low-maintenance alternative of spectroradiometers for accurate measurements of j(O1D) provided their spectral properties are known and potential drifts in sensitivities are monitored by regular calibrations with standard lamps or reference instruments