C-FOG Fernando, H. J. S.; Gultepe, I.; Dorman, C. ...
Bulletin of the American Meteorological Society,
02/2021, Letnik:
102, Številka:
2
Journal Article
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C-FOG is a comprehensive bi-national project dealing with the formation, persistence, and dissipation (life cycle) of fog in coastal areas (coastal fog) controlled by land, marine, and atmospheric ...processes. Given its inherent complexity, coastal-fog literature has mainly focused on case studies, and there is a continuing need for research that integrates across processes (e.g., air–sea–land interactions, environmental flow, aerosol transport, and chemistry), dynamics (two-phase flow and turbulence), microphysics (nucleation, droplet characterization), and thermodynamics (heat transfer and phase changes) through field observations and modeling. Central to C-FOG was a field campaign in eastern Canada from 1 September to 8 October 2018, covering four land sites in Newfoundland and Nova Scotia and an adjacent coastal strip transected by the Research Vessel Hugh R. Sharp. An array of in situ, path-integrating, and remote sensing instruments gathered data across a swath of space–time scales relevant to fog life cycle. Satellite and reanalysis products, routine meteorological observations, numerical weather prediction model (WRF and COAMPS) outputs, large-eddy simulations, and phenomenological modeling underpin the interpretation of field observations in a multiscale and multiplatform framework that helps identify and remedy numerical model deficiencies. An overview of the C-FOG field campaign and some preliminary analysis/findings are presented in this paper.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
THE MATERHORN Fernando, H. J. S.; Pardyjak, E. R.; Di Sabatino, S. ...
Bulletin of the American Meteorological Society,
11/2015, Letnik:
96, Številka:
11
Journal Article
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Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain ...meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multiinstitutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Force Fluctuations in Bead Packs C.-h. Liu; Nagel, S. R.; Schecter, D. A. ...
Science (American Association for the Advancement of Science),
07/1995, Letnik:
269, Številka:
5223
Journal Article
Recenzirano
Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially ...rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.
Now that it is possible to achieve measurement and control fidelities for individual quantum bits (qubits) above the threshold for fault tolerance, attention is moving towards the difficult task of ...scaling up the number of physical qubits to the large numbers that are needed for fault-tolerant quantum computing. In this context, quantum-dot-based spin qubits could have substantial advantages over other types of qubit owing to their potential for all-electrical operation and ability to be integrated at high density onto an industrial platform. Initialization, readout and single- and two-qubit gates have been demonstrated in various quantum-dot-based qubit representations. However, as seen with small-scale demonstrations of quantum computers using other types of qubit, combining these elements leads to challenges related to qubit crosstalk, state leakage, calibration and control hardware. Here we overcome these challenges by using carefully designed control techniques to demonstrate a programmable two-qubit quantum processor in a silicon device that can perform the Deutsch-Josza algorithm and the Grover search algorithm-canonical examples of quantum algorithms that outperform their classical analogues. We characterize the entanglement in our processor by using quantum-state tomography of Bell states, measuring state fidelities of 85-89 per cent and concurrences of 73-82 per cent. These results pave the way for larger-scale quantum computers that use spins confined to quantum dots.
The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest ...in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).
Decades of research suggest that social support is an important factor in predicting suicide risk and resilience. However, no studies have examined dynamic fluctuations in day-by-day levels of ...perceived social support. We examined such fluctuations over 28 days among a sample of 53 adults who attempted suicide in the past year (992 total observations). Variability in social support was analyzed with between-person intraclass correlations and root mean square of successive differences. Multi-level models were conducted to determine the association between social support and suicidal ideation. Results revealed that social support varies considerably from day to day with 45% of social support ratings differing by at least one standard deviation from the prior assessment. Social support is inversely associated with same-day and next-day suicidal ideation, but not with next-day suicidal ideation after adjusting for same-day suicidal ideation (i.e., not with daily changes in suicidal ideation). These results suggest that social support is a time-varying protective factor for suicidal ideation.
•Social support is considered an important factor in predicting suicide risk and resilience.•Among recent suicide attempters, social support varied from day to day.•Social support predicted suicidal ideation, but not daily changes in suicidal ideation.•Among recent suicide attempters, social support may be a dynamic protective factor.
Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment. The outstanding challenge is to ...engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet, and the spin state is read out in the single-shot mode. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots, whereas gate operation times are comparable to those reported in GaAs. The spin echo decay time is ~40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.
Sleep problems are transdiagnostic symptoms that confer significant risk for suicidal thoughts and behaviors (STBs) in adults. However, less is known about the sleep-STB association in adolescence—a ...developmental period when rates of STBs increase drastically, and sleep problems may be particularly pernicious. This article provides a systematic review of research on the sleep-STB association in youth, an overview of changes in sleep regulation during adolescence that may make sleep problems particularly detrimental for youth, and a discussion of the clinical implications of the sleep-STB association for hospitalized youth.
The systematic review included all longitudinal studies in which sleep problems were examined as prospective predictors of STBs in adolescents (aged 10–24 years). The search was conducted on December 1, 2017 using PsychINFO, PubMed, and Web of Science databases.
Ten studies qualified for inclusion in this review. Of these, seven studies found at least one type of sleep problem significantly predicted a STB outcome.
Although findings are mixed, growing research suggests that sleep problems may be a unique risk factor for STBs in youth. Sleep problems may be particularly important intervention target because they are easily assessed across healthcare settings and are amenable to treatment.
The qubit is the fundamental building block of a quantum computer. We fabricate a qubit in a silicon double-quantum dot with an integrated micromagnet in which the qubit basis states are the singlet ...state and the spin-zero triplet state of two electrons. Because of the micromagnet, the magnetic field difference Δ B between the two sides of the double dot is large enough to enable the achievement of coherent rotation of the qubit’s Bloch vector around two different axes of the Bloch sphere. By measuring the decay of the quantum oscillations, the inhomogeneous spin coherence time Formula is determined. By measuring Formula at many different values of the exchange coupling J and at two different values of Δ B , we provide evidence that the micromagnet does not limit decoherence, with the dominant limits on Formula arising from charge noise and from coupling to nuclear spins.
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