4,688 research outputs found
Building one molecule from a reservoir of two atoms
Chemical reactions typically proceed via stochastic encounters between
reactants. Going beyond this paradigm, we combine exactly two atoms into a
single, controlled reaction. The experimental apparatus traps two individual
laser-cooled atoms (one sodium and one cesium) in separate optical tweezers and
then merges them into one optical dipole trap. Subsequently, photoassociation
forms an excited-state NaCs molecule. The discovery of previously unseen
resonances near the molecular dissociation threshold and measurement of
collision rates are enabled by the tightly trapped ultracold sample of atoms.
As laser-cooling and trapping capabilities are extended to more elements, the
technique will enable the study of more diverse, and eventually more complex,
molecules in an isolated environment, as well as synthesis of designer
molecules for qubits
3D MHD Flux Emergence Experiments: Idealized models and coronal interactions
This paper reviews some of the many 3D numerical experiments of the emergence
of magnetic fields from the solar interior and the subsequent interaction with
the pre-existing coronal magnetic field. The models described here are
idealized, in the sense that the internal energy equation only involves the
adiabatic, Ohmic and viscous shock heating terms. However, provided the main
aim is to investigate the dynamical evolution, this is adequate. Many
interesting observational phenomena are explained by these models in a
self-consistent manner.Comment: Review article, accepted for publication in Solar Physic
Perspectives of Statistician, Microbiologist, and Clinician Stakeholders on the Use of Microbiological Outcomes in Randomised Trials of Antimicrobial Stewardship Interventions
Microbiological data are used as indicators of infection, for diagnosis, and the identification
of antimicrobial resistance in trials of antimicrobial stewardship interventions. However, several
problems have been identified in a recently conducted systematic review (e.g., inconsistency in
reporting and oversimplified outcomes), which motivates the need to understand and improve the use
of these data including analysis and reporting. We engaged key stakeholders including statisticians,
clinicians from both primary and secondary care, and microbiologists. Discussions included issues
identified in the systematic review and questions about the value of using microbiological data in
clinical trials, perspectives on current microbiological outcomes reported in trials, and alternative
statistical approaches to analyse these data. Various factors (such as unclear sample collection process,
dichotomising or categorising complex microbiological data, and unclear methods of handling
missing data) were identified that contributed to the low quality of the microbiological outcomes and
the analysis of these outcomes in trials. Whilst not all of these factors would be easy to overcome,
there is room for improvement and a need to encourage researchers to understand the impact of
misusing these data. This paper discusses the experience and challenges of using microbiological
outcomes in clinical trials
Enhancement of mechanical Q-factors by optical trapping
The quality factor of a mechanical resonator is an important figure of merit
for various sensing applications and for observing quantum behavior. Here, we
demonstrate a technique to push the quality factor of a micro-mechanical
resonator beyond conventional material and fabrication limits by using an
optical field to stiffen or "trap" a particular motional mode. Optical forces
increase the oscillation frequency by storing most of the mechanical energy in
a lossless optical potential, thereby strongly diluting the effect of material
dissipation. By using a 130 nm thick SiO disk as a suspended pendulum, we
achieve an increase in the pendulum center-of-mass frequency from 6.2 kHz to
145 kHz. The corresponding quality factor increases 50-fold from its intrinsic
value to a final value of , representing more than an
order of magnitude improvement over the conventional limits of SiO for this
geometry. Our technique may enable new opportunities for mechanical sensing and
facilitate observations of quantum behavior in this class of mechanical
systems.Comment: 14 pages, 4 figure
Assessment of workpiece surface integrity and dimensional/geometrical accuracy following finish plunge end milling of holes drilled with worn tools in PM-processed nickel based superalloy
Powder metallurgy (PM) processed nickel-based superalloys are increasingly employed in the hot section of gas turbine engines for parts such as high-pressure (HP) compressors and turbine rotor discs over more traditional cast and wrought options such as Inconel 718 due to its improved high-temperature properties. In this paper, the surface integrity and geometrical/dimensional accuracy of holes initially rough drilled using worn tools and subsequently finish plunge end milled in a proprietary PM-processed Ni-based superalloy, were assessed and compared. The influence of tool wear on hole quality after finish plunge end milling was also investigated. Significant improvement in hole quality was evident following finishing with reductions in surface roughness (up to ~86%), subsurface microhardness (up to ~125 HK0.05) and workpiece microstructure deformation/damage (up to ~80% in terms of average depth) compared to corresponding rough drilled holes. Evidence of chatter marks on holes machined with worn plunge end mills was observed, despite exhibiting reduced surface roughness levels (~45-73%). Generally, somewhat improved hole surface integrity (reduced subsurface deformation by ~47-64%) and geometrical accuracy (circularity decreased by ~10-25%) were produced when employing new tools.</p
Inferring Airflow Across Martian Dunes From Ripple Patterns and Dynamics
Large ripples form striking patterns on the slopes of martian sand dunes which can be mapped and tracked using high-resolution optical images. The ripples vary in orientation, wavelength, plan-view morphology, and rates of migration. The variations in the ripple patterns are recognized to signal the effects of the regional and local winds and feedbacks between winds and dune topography. We examine the ripple patterns and the motion of these ripples to interpret airflow dynamics around dunes in the dune field at Nili Patera. We find that coincident changes in ripple patterns and migration rates in dune wakes indicate reattachment lengths of 4–7 brink heights. This reattachment length is similar to length scales of flow reattachment for airflow over dunes measured on Earth despite the differences in aeolian environment. Furthermore, ripples on dune flanks are shown to behave according to terrestrial models for ripple development on steep slopes. Compensating for these slope effects allows them to act as indicators of dune-modified and regional wind directions. Changes in ripple patterns and migration rates also signal the response of dunes and airflow during dune collisions. Collectively, we find that differences in ripple patterns connected to changes in migration rate provide information on airflow over and around dunes. This detailed assessment of ripple measurement and ripple migration rates advances the use of ripples on martian dunes and sand sheets to infer dune- and field-scale wind dynamics. These measurements also indicate that the low density atmosphere on Mars does not significantly modify the behavior of wind-topography interactions compared to Earth. Such observations provide targets for computational fluid dynamic and large-eddy simulation models seeking to reveal complex airflows across dune fields both on Earth and on Mars
Long-term management of generalised anxiety disorder with low-dose continuous infusions of flumazenil: A case series
Background: Generalised anxiety disorder (GAD) is a common anxiety disorder associated with social and occupational impairment. Recently, a theory was postulated that dysfunctional gamma aminobutyric acid type A receptors (GABAA) are implicated in anxiety symptomology, which could be corrected by flumazenil, an antagonist at the benzodiazepine binding site on the GABAA receptor. Method: Participants had a primary diagnosis of GAD and were treated initially with an eight-day continuous low-dose flumazenil infusion (total 32 mg at a rate of 4 mg/24 h). Some participants were re-treated with a further four- or eight-day infusion. Treatment response was measured as a 50 % reduction in anxiety or stress scores on the Depression Anxiety Stress Scale — 21 (DASS-21). Remission was measured as scores ≤ 3 or ≤ 7 on the anxiety and stress subscales of the DASS-21, respectively. Results: Eight cases are reported. All cases met the criteria for treatment response on the anxiety and stress subscale of the DASS-21. Remission was achieved in seven participants on the anxiety subscale and in five on the stress subscale. No changes in hepatic, renal, or haematological function were likely attributed to flumazenil. Conclusion: Data suggest that low-dose continuous flumazenil infusion manages GAD symptoms and is safe. Although these results are promising, future randomised control trials are required to confirm these results
Unmanned Aircraft Systems in the Cyber Domain
Unmanned Aircraft Systems are an integral part of the US national critical infrastructure. The authors have endeavored to bring a breadth and quality of information to the reader that is unparalleled in the unclassified sphere. This textbook will fully immerse and engage the reader / student in the cyber-security considerations of this rapidly emerging technology that we know as unmanned aircraft systems (UAS). The first edition topics covered National Airspace (NAS) policy issues, information security (INFOSEC), UAS vulnerabilities in key systems (Sense and Avoid / SCADA), navigation and collision avoidance systems, stealth design, intelligence, surveillance and reconnaissance (ISR) platforms; weapons systems security; electronic warfare considerations; data-links, jamming, operational vulnerabilities and still-emerging political scenarios that affect US military / commercial decisions.
This second edition discusses state-of-the-art technology issues facing US UAS designers. It focuses on counter unmanned aircraft systems (C-UAS) – especially research designed to mitigate and terminate threats by SWARMS. Topics include high-altitude platforms (HAPS) for wireless communications; C-UAS and large scale threats; acoustic countermeasures against SWARMS and building an Identify Friend or Foe (IFF) acoustic library; updates to the legal / regulatory landscape; UAS proliferation along the Chinese New Silk Road Sea / Land routes; and ethics in this new age of autonomous systems and artificial intelligence (AI).https://newprairiepress.org/ebooks/1027/thumbnail.jp
Counter Unmanned Aircraft Systems Technologies and Operations
As the quarter-century mark in the 21st Century nears, new aviation-related equipment has come to the forefront, both to help us and to haunt us. (Coutu, 2020) This is particularly the case with unmanned aerial vehicles (UAVs). These vehicles have grown in popularity and accessible to everyone. Of different shapes and sizes, they are widely available for purchase at relatively low prices. They have moved from the backyard recreation status to important tools for the military, intelligence agencies, and corporate organizations. New practical applications such as military equipment and weaponry are announced on a regular basis – globally. (Coutu, 2020) Every country seems to be announcing steps forward in this bludgeoning field.
In our successful 2nd edition of Unmanned Aircraft Systems in the Cyber Domain: Protecting USA’s Advanced Air Assets (Nichols, et al., 2019), the authors addressed three factors influencing UAS phenomena. First, unmanned aircraft technology has seen an economic explosion in production, sales, testing, specialized designs, and friendly / hostile usages of deployed UAS / UAVs / Drones. There is a huge global growing market and entrepreneurs know it. Second, hostile use of UAS is on the forefront of DoD defense and offensive planners. They are especially concerned with SWARM behavior. Movies like “Angel has Fallen,” where drones in a SWARM use facial recognition technology to kill USSS agents protecting POTUS, have built the lore of UAS and brought the problem forefront to DHS. Third, UAS technology was exploding. UAS and Counter- UAS developments in navigation, weapons, surveillance, data transfer, fuel cells, stealth, weight distribution, tactics, GPS / GNSS elements, SCADA protections, privacy invasions, terrorist uses, specialized software, and security protocols has exploded. (Nichols, et al., 2019) Our team has followed / tracked joint ventures between military and corporate entities and specialized labs to build UAS countermeasures.
As authors, we felt compelled to address at least the edge of some of the new C-UAS developments. It was clear that we would be lucky if we could cover a few of – the more interesting and priority technology updates – all in the UNCLASSIFIED and OPEN sphere.
Counter Unmanned Aircraft Systems: Technologies and Operations is the companion textbook to our 2nd edition. The civilian market is interesting and entrepreneurial, but the military and intelligence markets are of concern because the US does NOT lead the pack in C-UAS technologies. China does. China continues to execute its UAS proliferation along the New Silk Road Sea / Land routes (NSRL). It has maintained a 7% growth in military spending each year to support its buildup. (Nichols, et al., 2019) [Chapter 21]. They continue to innovate and have recently improved a solution for UAS flight endurance issues with the development of advanced hydrogen fuel cell. (Nichols, et al., 2019) Reed and Trubetskoy presented a terrifying map of countries in the Middle East with armed drones and their manufacturing origin. Guess who? China. (A.B. Tabriski & Justin, 2018, December)
Our C-UAS textbook has as its primary mission to educate and train resources who will enter the UAS / C-UAS field and trust it will act as a call to arms for military and DHS planners.https://newprairiepress.org/ebooks/1031/thumbnail.jp
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