Drivers of Sediment Transport Across the Entrance to the Gippsland Lakes, Australia

Water Qualit

The Phantom Divide in String Gas Cosmology

One of the main virtues of string gas cosmology is that it resolves cosmological singularities. Since the Universe can be approximated by a locally asymptotically de Sitter spacetime by the end of the inflationary era, a singularity theorem implies that these cosmologies effectively violate the Null Energy Condition [not just the Strong Energy Condition]. We stress that this is an extremely robust result, which does not depend on assuming that the spatial sections remain precisely flat in the early Universe. This means, however, that it must be possible for string cosmologies to cross the recently much-discussed "phantom divide" [from w -1, where w is the equation-of-state parameter]. This naturally raises the question as to whether the phantom divide can be crossed again, to account for recent observations suggesting that w < -1 at the present time. We argue that non-perturbative string effects rule out this possibility, even if the NEC violation in question is only "effective".Comment: 29 pages, 5 eps figures, references adde

Frame-by-frame annotation of video recordings using deep neural networks

Funding: Scottish Government (Grant Number(s): Marine Mammal Scientific Support Research Program); Homebrew Films; National Research Foundation of South Africa (Grant Number(s): 105782, 90782).Video data are widely collected in ecological studies, but manual annotation is a challenging and time‐consuming task, and has become a bottleneck for scientific research. Classification models based on convolutional neural networks (CNNs) have proved successful in annotating images, but few applications have extended these to video classification. We demonstrate an approach that combines a standard CNN summarizing each video frame with a recurrent neural network (RNN) that models the temporal component of video. The approach is illustrated using two datasets: one collected by static video cameras detecting seal activity inside coastal salmon nets and another collected by animal‐borne cameras deployed on African penguins, used to classify behavior. The combined RNN‐CNN led to a relative improvement in test set classification accuracy over an image‐only model of 25% for penguins (80% to 85%), and substantially improved classification precision or recall for four of six behavior classes (12–17%). Image‐only and video models classified seal activity with very similar accuracy (88 and 89%), and no seal visits were missed entirely by either model. Temporal patterns related to movement provide valuable information about animal behavior, and classifiers benefit from including these explicitly. We recommend the inclusion of temporal information whenever manual inspection suggests that movement is predictive of class membership.Publisher PDFPeer reviewe

Pre-Inflationary Spacetime in String Cosmology

Seiberg and Witten have shown that the non-perturbative stability of string physics on conformally compactified spacetimes is related to the behaviour of the areas and volumes of certain branes as the brane is moved towards infinity. If, as is particularly natural in quantum cosmology, the spatial sections of an accelerating cosmological model are flat and compact, then the spacetime is on the brink of disaster: it turns out that the version of inflationary spacetime geometry with toral spatial sections is marginally stable in the Seiberg-Witten sense. The question is whether the system remains stable before and after Inflation, when the spacetime geometry is distorted away from the inflationary form but still has flat spatial sections. We show that it is indeed possible to avoid disaster, but that requiring stability at all times imposes non-trivial conditions on the spacetime geometry of the early Universe in string cosmology. This in turn allows us to suggest a candidate for the structure which, in the earliest Universe, forbids cosmological singularities.Comment: Final version to appear in NPB, 27 pages including 1 eps figur

The Most Probable Size of the Universe

It has recently been suggested, by Firouzjahi, Sarangi, and Tye, that string-motivated modifications of the Hartle-Hawking wave function predict that our Universe came into existence from "nothing" with a de Sitter-like spacetime geometry and a spacetime curvature similar to that of "low-scale" models of Inflation. This means, however, that the Universe was quite large at birth. It would be preferable for the initial scale to be close to the string scale, or perhaps the Planck scale. The problem with this, however, is to explain how any initial homogeneity is preserved during the pre-inflationary era, so that Inflation can indeed begin. Here we modify a suggestion due to Linde and assume that the Universe was born with the topology of a torus; however, we propose that the size of the torus is to be predicted by the FST wave function. The latter does predict an initial size for the torus at about the string scale, and it also predicts a pre-inflationary spacetime geometry such that chaotic mixing preserves any initial homogeneity until Inflation can begin at a relatively low scale.Comment: References added; accepted by Nuclear Physics

Prediction and benefits of minimal disease activity in patients with psoriatic arthritis and active skin disease in the ADEPT trial

Objectives: To determine the proportion of patients with psoriatic arthritis in the Adalimumab Effectiveness in Psoriatic Arthritis trial achieving minimal disease activity (MDA) and its individual components at 1 or more visits over 144 weeks, identify baseline predictors of MDA achievement, and evaluate the association of MDA status with independent quality of life (QoL)-related patient-reported outcomes (PROs). Methods: Univariate and multivariate analyses were used to identify the baseline characteristics that predicted achievement of MDA at individual time points (weeks 12 through 144) or sustained MDA (achievement of MDA at 2 consecutive time points 12 weeks apart). The association of independent QoL-related PROs with MDA achievement was evaluated at weeks 24 and 144. Results: In univariate analyses, higher baseline patient assessment of pain, tender joint count (TJC), enthesitis and Health Assessment Questionnaire-Disability Index (HAQ-DI) score were significantly associated with lower likelihood of achieving MDA at later time points. Multivariate analyses confirmed higher baseline HAQ-DI as a significant predictor for failure to achieve MDA at later time points. Achievement of sustained MDA was associated with lower baseline TJC and HAQ-DI score. Achievement of different MDA components appeared to be treatment dependent. MDA achievers had significantly better QoL-related PROs and greater improvements in PROs from baseline to week 24 compared with non-achievers. Conclusions: Higher HAQ-DI score was the most consistent baseline factor that decreased the likelihood of achieving MDA and sustained MDA at later time points. Achieving MDA was associated with better independent QoL-related PROs

An inverted-sandwich diuranium μ-η5:η5-cyclo-P5 complex supported by U-P5 δ-bonding

Reaction of [U(TrenTIPS)] [1, TrenTIPS=N(CH2CH2NSiiPr3)3] with 0.25 equivalents of P4 reproducibly affords the unprecedented actinide inverted sandwich cyclo-P5 complex [{U(TrenTIPS)}2(μ-η5:η5-cyclo-P5)] (2). All prior examples of cyclo-P5 are stabilized by d-block metals, so 2 shows that cyclo-P5 does not require d-block ions to be prepared. Although cyclo-P5 is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P5)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo-P5 charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P5 compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals

Synthesis and characterization of an f‑block terminal parent imido [U=NH] complex: a masked uranium(IV) nitride

Deprotonation of [U(TrenTIPS)(NH2)] (1) [TrenTIPS = N(CH2CH2NSiPri3)3] with organoalkali metal reagents MR (M = Li, R = But; M = Na−Cs, R = CH2C6H5) afforded the imido-bridged dimers [{U-(TrenTIPS)(μ-N[H]M)}2] [M = L −Cs (2a−e)]. Treatmentof 2c (M = K) with 2 equiv of 15 crown-5 ether (15C5) afforded the uranium terminal parent imido complex [U(TrenTIPS)(NH)][K(15C5)2] (3c), which can also be viewed as a masked uranium(IV) nitride. The uranium−imido linkage was found to be essentially linear, and theoretical calculations suggested σ2π4 polarized U−N multiple bonding. Attempts to oxidize 3c to afford the neutral uranium terminal parent imido complex [U(TrenTIPS)(NH)] (4) resulted in spontaneous disproportionation to give 1 and the uranium−nitride complex [U(TrenTIPS)(N)] (5); this reaction is a new way to prepare the terminal uranium−nitride linkage and was calculated to be exothermic by −3.25 kcal mol−1

Scalar field instability in de Sitter space-time

Starting from the equation of motion of the quantum operator of a real scalar field phi in de Sitter space-time, a simple differential equation is derived which describes the evolution of quantum fluctuations of this field. Full de Sitter invariance is assumed and no ad hoc infrared cutoff is introduced. This equation is solved explicitly and in massive case our result agrees with the standard one. In massless case the large time behavior of our solution differs by sign from the expression found in earlier papers. A possible cause of discrepancy may be a spontaneous breaking of de Sitter invariance.Comment: 20 pages, no figures, revtex4. V2: minor changes, references adde

Isolation of elusive HAsAsH in a crystalline diuranium(IV) complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short-lived species generated in electrochemical or microwave-plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(TrenTIPS)}2(μ-η2:η2-As2H2)] (3, TrenTIPS=N(CH2CH2NSiPri3)3; Pri=CH(CH3)2). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back-bonding-type interactions from uranium to the HAsAsH π*-orbital. This experimentally confirms the theoretically predicted excellent π-acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane-1,2-diide form