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Close-range sensors are employed to observe glaciological processes that operate over short timescales (e.g. iceberg calving, glacial lake outburst floods, diurnal surface melting). However, under poor weather conditions optical instruments fail while the operation of radar systems below 17 GHz do not have sufficient angular resolution to map glacier surfaces in detail. This letter reviews the potential of millimetre-wave radar at 94 GHz to obtain high-resolution 3-D measurements of glaciers under most weather conditions. We discuss the theory of 94 GHz radar for glaciology studies, demonstrate its potential to map a glacier calving front and summarise future research priorities.
Serpent Mound, in northern Adams County, Ohio, USA, is one of the most iconic symbols of ancient America and yet there is no widely agreed upon date for the age of its original construction. Some archaeologists consider it to have been built by the Adena culture around 300 bc, while others contend it was built by the Fort Ancient culture around ad 1100. There have been three attempts to obtain radiometric ages for the effigy, but they have yielded inconclusive results. The iconography of the earthwork offers an alternative means of placing the mound in its cultural context. Serpent imagery is abundant in the Fort Ancient culture as well as in the more encompassing Mississippian Ideological Interaction Sphere. Pictographs from Picture Cave in Missouri include a serpent, a humanoid female and a vulvoid in close association. We interpret these elements, in the light of Siouan oral traditions, as First Woman and her consort the Great Serpent. The Picture Cave imagery dates to between ad 950 and 1025. We argue that these same three elements are represented in the original configuration of Serpent Mound and therefore situate its design and original construction in the Early Fort Ancient period.
Measurements of glacier ice cliff evolution are sparse, but where they do exist, they indicate that such areas of exposed ice contribute a disproportionate amount of melt to the glacier ablation budget. We used Structure from Motion photogrammetry with Multi-View Stereo to derive 3-D point clouds for nine ice cliffs on Khumbu Glacier, Nepal (in November 2015, May 2016 and October 2016). By differencing these clouds, we could quantify the magnitude, seasonality and spatial variability of ice cliff retreat. Mean retreat rates of 0.30–1.49 cm d−1 were observed during the winter interval (November 2015–May 2016) and 0.74–5.18 cm d−1 were observed during the summer (May 2016–October 2016). Four ice cliffs, which all featured supraglacial ponds, persisted over the full study period. In contrast, ice cliffs without a pond or with a steep back-slope degraded over the same period. The rate of thermo-erosional undercutting was over double that of subaerial retreat. Overall, 3-D topographic differencing allowed an improved process-based understanding of cliff evolution and cliff-pond coupling, which will become increasingly important for monitoring and modelling the evolution of thinning debris-covered glaciers.
This book presents a wide range of new research on many aspects of naval strategy in the early modern and modern periods. Among the themes covered are the problems of naval manpower, the nature of naval leadership and naval officers, intelligence, naval training and education, and strategic thinking and planning. The book is notable for giving extensive consideration to navies other than those ofBritain, its empire and the United States. It explores a number of fascinating subjects including how financial difficulties frustrated the attempts by Louis XIV's ministers to build a strong navy; how the absence of centralised power in the Dutch Republic had important consequences for Dutch naval power; how Hitler's relationship with his admirals severely affected German naval strategy during the Second World War; and many more besides. The book is a Festschrift in honour of John B. Hattendorf, for more than thirty years Ernest J. King Professor of Maritime History at the US Naval War College and an influential figure in naval affairs worldwide.
N.A.M. Rodger is Senior Research Fellow at All Souls College, Oxford.
J. Ross Dancy is Assistant Professor of Military History at Sam Houston State University.
Benjamin Darnell is a D.Phil. candidate at New College, Oxford.
Evan Wilson is Caird Senior Research Fellow at the National Maritime Museum, Greenwich.
Contributors: Tim Benbow, Peter John Brobst, Jaap R. Bruijn, Olivier Chaline, J. Ross Dancy, Benjamin Darnell, James Goldrick, Agustín Guimerá, Paul Kennedy, Keizo Kitagawa, Roger Knight, Andrew D. Lambert, George C. Peden, Carla Rahn Phillips, Werner Rahn, Paul M. Ramsey, Duncan Redford, N.A.M. Rodger, Jakob Seerup, Matthew S. Seligmann, Geoffrey Till, Evan Wilson
The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae, and orphan afterglows of gamma-ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of 5 s and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.
A series of editorials in this Journal have argued that psychiatry is in the midst of a crisis. The various solutions proposed would all involve a strengthening of psychiatry's identity as essentially ‘applied neuroscience’. Although not discounting the importance of the brain sciences and psychopharmacology, we argue that psychiatry needs to move beyond the dominance of the current, technological paradigm. This would be more in keeping with the evidence about how positive outcomes are achieved and could also serve to foster more meaningful collaboration with the growing service user movement.
A theoretical model is presented for the generation of waves by a localized pressure distribution moving on the surface of deep water with speed near the minimum gravity–capillary phase speed, cmin. The model employs a simple forced–damped nonlinear dispersive equation. Even though it is not formally derived from the full governing equations, the proposed model equation combines the main effects controlling the response and captures the salient features of the experimental results reported in Diorio et al. (J. Fluid Mech., vol. 672, 2011, pp. 268–287 – Part 1 of this work). Specifically, as the speed of the pressure disturbance is increased towards cmin, three distinct responses arise: state I is confined beneath the applied pressure and corresponds to the linear subcritical steady solution; state II is steady, too, but features a steep gravity–capillary lump downstream of the pressure source; and state III is time-periodic, involving continuous shedding of lumps downstream. The transitions from states I to II and from states II to III, observed experimentally, are associated with certain limit points in the steady-state response diagram computed via numerical continuation. Moreover, within the speed range that state II is reached, the maximum response amplitude turns out to be virtually independent of the strength of the pressure disturbance, in agreement with the experiment. The proposed model equation, while ad hoc, brings out the delicate interplay between dispersive, nonlinear and viscous effects that takes place near cmin, and may also prove useful in other physical settings where a phase-speed minimum at non-zero wavenumber occurs.
The wave pattern generated by a pressure source moving over the free surface of deep water at speeds, U, below the minimum phase speed for linear gravity–capillary waves, cmin, was investigated experimentally using a combination of photographic measurement techniques. In similar experiments, using a single pressure amplitude, Diorio et al. (Phys. Rev. Lett., vol. 103, 2009, 214502) pointed out that the resulting surface response pattern exhibits remarkable nonlinear features as U approaches cmin, and three distinct response states were identified. Here, we present a set of measurements for four surface-pressure amplitudes and provide a detailed quantitative examination of the various behaviours. At low speeds, the pattern resembles the stationary state (U = 0), essentially a circular dimple located directly under the pressure source (called a state I response). At a critical speed, but still below cmin, there is an abrupt transition to a wave-like state (state II) that features a marked increase in the response amplitude and the formation of a localized solitary depression downstream of the pressure source. This solitary depression is steady, elongated in the cross-stream relative to the streamwise direction, and resembles freely propagating gravity–capillary ‘lump’ solutions of potential flow theory on deep water. Detailed measurements of the shape of this depression are presented and compared with computed lump profiles from the literature. The amplitude of the solitary depression decreases with increasing U (another known feature of lumps) and is independent of the surface pressure magnitude. The speed at which the transition from states I to II occurs decreases with increasing surface pressure. For speeds very close to the transition point, time-dependent oscillations are observed and their dependence on speed and pressure magnitude are reported. As the speed approaches cmin, a second transition is observed. Here, the steady solitary depression gives way to an unsteady state (state III), characterized by periodic shedding of lump-like disturbances from the tails of a V-shaped pattern.
Previous cross-sectional study of ventral prefrontal cortex (VPFC) implicated progressive volume abnormalities during adolescence in bipolar disorder (BD). In the present study, a within-subject, longitudinal design was implemented to examine brain volume changes during adolescence/young adulthood. We hypothesized that VPFC volume decreases over time would be greater in adolescents/young adults with BD than in healthy comparison adolescents/young adults. Eighteen adolescents/young adults (10 with BD I and 8 healthy comparison participants) underwent two high-resolution magnetic resonance imaging scans over approximately 2 years. Regional volume changes over time were measured. Adolescents/young adults with BD displayed significantly greater volume loss over time, compared to healthy comparison participants, in a region encompassing VPFC and rostral PFC and extending to rostral anterior cingulate cortex (p < .05). Additional areas where volume change differed between groups were observed. While data should be interpreted cautiously due to modest sample size, this study provides preliminary evidence to support the presence of accelerated loss in VPFC and rostral PFC volume in adolescents/young adults with BD. (JINS, 2009, 15, 476–481.)