772 research outputs found
Minimum Cost of Transport in Asian Elephants: Do We Really Need a Bigger Elephant?
Body mass is the primary determinant of an animal’s energy requirements. At their optimum walking speed, large animals have lower mass-specific energy requirements for locomotion than small ones. In animals ranging in size from 0.8 g (roach) to 260 kg (zebu steer), the minimum cost of transport (COTmin) decreases with increasing body size roughly as COTmin∝body mass (Mb)–0.316±0.023 (95% CI). Typically, the variation of COTmin with body mass is weaker at the intraspecific level as a result of physiological and geometric similarity within closely related species. The interspecific relationship estimates that an adult elephant, with twice the body mass of a mid-sized elephant, should be able to move its body approximately 23% cheaper than the smaller elephant. We sought to determine whether adult Asian and sub-adult African elephants follow a single quasi-intraspecific relationship, and extend the interspecific relationship between COTmin and body mass to 12-fold larger animals. Physiological and possibly geometric similarity between adult Asian elephants and sub-adult African elephants caused body mass to have a no effect on COTmin (COTmin∝Mb0.007±0.455). The COTmin in elephants occurred at walking speeds between 1.3 and ∼1.5 m s–1, and at Froude numbers between 0.10 and 0.24. The addition of adult Asian elephants to the interspecific relationship resulted in COTmin∝M –0.277±0.046b. The quasi-intraspecific relationship between body mass and COTmin among elephants caused the interspecific relationship to underestimate COTmin in larger elephants
Recommended from our members
Accounting for employment outcomes following traumatic brain injury (TBI): The implications for delivering TBI vocational rehabilitation in the UK
This thesis arises out of personal experience of the employment problems faced by people sustaining traumatic brain injury (TBI). Through tracking the post-injury experience of 54 subjects it aims to test the opinion that, generally, there is a lack of expert support to facilitate a return to work and, for young people, inadequate mechanisms to facilitate a transition from education into employment. In particular, it is maintained that generic vocational rehabilitation (VR) services provided by Jobcentre Plus fail to meet the needs of many TBI customers ( to use their terminology). In the circumstances it is contested that a return to work following TBI may follow a random pattern, but that an appropriate programme of VR, objectively identified within the thesis and based upon best practice and research based evidence, should improve resettlement rates.
Following a review of research methodologies commonly found in employment and disability studies the thesis relies upon a combined methodological strategy to test the above opinions. The literature review, and the experience of the study sample, are used to identify a) significant demographic and clinical variables to be taken into account when planning vocational intervention, b) difficulties in accessing appropriate VR programmes. A non-experimental survey research design relied on a fixed format questionnaire to collect study sample data, evaluated through the use of description and association statistics. Three case studies are further analysed through a realist approach identifying the circumstances in which measures taken to resume employment contributed to the final outcomes.
The thesis identifies an inaccurate recording of the brain-injured population within the DWP and a significant job retention problem amongst the study sample. It establishes why generic vocational rehabilitation services are failing this population and why many potentially employable people find themselves receiving long-term incapacity benefits.
The conclusion presents a theoretical model VR programme, deliverable within the context of current developments for joint NHS/Jobcentre Plus condition management (VR) programmes. It argues the case for TBI VR programmes in the UK moving away from a focus on pre-placement treatment and job-search activity towards one incorporating lengthy occupational trials and on-site support for both the employee and employer. It establishes the need for both ’joined-up’ services, from hospital to employment, and trained job coaches. Finally there are recommendations for enhancing future research in the employment and disability sector
Membrane-in-the-middle optomechanics with a soft-clamped membrane at milliKelvin temperatures
Soft-clamped silicon nitride membrane resonators reach coherence times tau in
excess of 100 ms at milliKelvin bath temperatures. However, harnessing strong
optomechanical coupling in dry dilution refrigerators remains challenging due
to vibration issues and heating by optical absorption. Here, we propose to
address these issues with an actuator-free optical cavity and mechanical
resonator design, in which the cavity is mounted on a simple
vibration-isolation platform. We observe dynamical backaction when the cavity
is driven with a free-space optical beam stabilized close to the red sideband
using a two-beam locking scheme. Finally, we characterize the effect of
absorption heating on the coherence time, and find a scaling with the
intracavity power P as tau proportional to P to the power of -(0.34+/-0.04)
Laser cooling a membrane-in-the-middle system close to the quantum ground state from room temperature
Many protocols in quantum science and technology require initializing a system in a pure quantum state. In the context of the motional state of massive resonators, this enables studying fundamental physics at the elusive quantum–classical transition, and measuring force and acceleration with enhanced sensitivity. Laser cooling has been a method of choice to prepare mechanical resonators in the quantum ground state, one of the simplest pure states. However, to overcome the heating and decoherence by the thermal bath, this usually has to be combined with cryogenic cooling. Here, we laser-cool an ultracoherent, soft-clamped mechanical resonator close to the quantum ground state directly from room temperature. To this end, we implement the versatile membrane-in-the-middle setup with one fiber mirror and one phononic crystal mirror, which reaches a quantum cooperativity close to unity already at room temperature. We furthermore introduce a powerful combination of coherent and measurement-based quantum control techniques, which allows us to mitigate thermal intermodulation noise. The lowest occupancy we reach is 30 phonons, limited by measurement imprecision. Doing away with the necessity for cryogenic cooling should further facilitate the spread of optomechanical quantum technologies
Rofecoxib and cardiovascular adverse events in adjuvant treatment of colorectal cancer
Background
Selective cyclooxygenase inhibitors may retard the progression of cancer, but they
have enhanced thrombotic potential. We report on cardiovascular adverse events in
patients receiving rofecoxib to reduce rates of recurrence of colorectal cancer.
Methods
All serious adverse events that were cardiovascular thrombotic events were reviewed
in 2434 patients with stage II or III colorectal cancer participating in a randomized,
placebo-controlled trial of rofecoxib, 25 mg daily, started after potentially curative
tumor resection and chemotherapy or radiotherapy as indicated. The trial was terminated
prematurely owing to worldwide withdrawal of rofecoxib. To examine possible
persistent risks, we examined cardiovascular thrombotic events reported up to 24
months after the trial was closed.
Results
The median duration of active treatment was 7.4 months. The 1167 patients receiving
rofecoxib and the 1160 patients receiving placebo were well matched, with a median
follow-up period of 33.0 months (interquartile range, 27.6 to 40.1) and 33.4 months
(27.7 to 40.4), respectively. Of the 23 confirmed cardiovascular thrombotic events,
16 occurred in the rofecoxib group during or within 14 days after the treatment
period, with an estimated relative risk of 2.66 (from the Cox proportional-hazards
model; 95% confidence interval [CI], 1.03 to 6.86; P = 0.04). Analysis of the Antiplatelet
Trialists’ Collaboration end point (the combined incidence of death from
cardiovascular, hemorrhagic, and unknown causes; of nonfatal myocardial infarction;
and of nonfatal ischemic and hemorrhagic stroke) gave an unadjusted relative
risk of 1.60 (95% CI, 0.57 to 4.51; P = 0.37). Fourteen more cardiovascular thrombotic
events, six in the rofecoxib group, were reported within the 2 years after trial
closure, with an overall unadjusted relative risk of 1.50 (95% CI, 0.76 to 2.94;
P = 0.24). Four patients in the rofecoxib group and two in the placebo group died
from thrombotic causes during or within 14 days after the treatment period, and
during the follow-up period, one patient in the rofecoxib group and five patients in
the placebo group died from cardiovascular causes.
Conclusions
Rofecoxib therapy was associated with an increased frequency of adverse cardiovascular
events among patients with a median study treatment of 7.4 months’ duration.
(Current Controlled Trials number, ISRCTN98278138.
Fate of Allochthonous Dissolved Organic Carbon in Lakes: A Quantitative Approach
Inputs of dissolved organic carbon (DOC) to lakes derived from the surrounding landscape can be stored, mineralized or passed to downstream ecosystems. The balance among these OC fates depends on a suite of physical, chemical, and biological processes within the lake, as well as the degree of recalcintrance of the allochthonous DOC load. The relative importance of these processes has not been well quantified due to the complex nature of lakes, as well as challenges in scaling DOC degradation experiments under controlled conditions to the whole lake scale. We used a coupled hydrodynamic-water quality model to simulate broad ranges in lake area and DOC, two characteristics important to processing allochthonous carbon through their influences on lake temperature, mixing depth and hydrology. We calibrated the model to four lakes from the North Temperate Lakes Long Term Ecological Research site, and simulated an additional 12 ‘hypothetical’ lakes to fill the gradients in lake size and DOC concentration. For each lake, we tested several mineralization rates (range: 0.001 d−1 to 0.010 d−1) representative of the range found in the literature. We found that mineralization rates at the ecosystem scale were roughly half the values from laboratory experiments, due to relatively cool water temperatures and other lake-specific factors that influence water temperature and hydrologic residence time. Results from simulations indicated that the fate of allochthonous DOC was controlled primarily by the mineralization rate and the hydrologic residence time. Lakes with residence times <1 year exported approximately 60% of the DOC, whereas lakes with residence times >6 years mineralized approximately 60% of the DOC. DOC fate in lakes can be determined with a few relatively easily measured factors, such as lake morphometry, residence time, and temperature, assuming we know the recalcitrance of the DOC
A model for hysteretic magnetic properties under the application of noncoaxial stress and field
Although descriptions of the effect of stress on spontaneous magnetization within a single domain already exist, there remains no adequate mathematical model for the effects of noncoaxial magnetic field and stress on bulk magnetization in a multidomained specimen. This article addresses the problem and provides a phenomenological theory that applies to the case of bulk isotropic materials. The magnetomechanical hysteresis model of Sablik and Jiles is thus extended to treat magnetic properties in the case of noncoaxial stress and magnetic field in an isotropic, polycrystalline medium. In the modeling, noncollinearity between magnetization and magnetic field is taken into account. The effect of roll‐axis anisotropy is also considered. Both magnetic and magnetostrictive hysteresis are describable by the extended model. Emphasis in this article is on describing properties like coercivity, remanence,hysteresis loss, maximum flux density, and maximum differential permeability as a function of stress for various angular orientations between field and stress axis. The model predictions are compared with experimental results
A titanium-nitride near-infrared kinetic inductance photon-counting detector and its anomalous electrodynamics
We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN)
microwave kinetic inductance detectors. Energy resolution of 0.4 eV and
arrival-time resolution of 1.2 microseconds are achieved. 0-, 1-, 2-photon
events are resolved and shown to follow Poisson statistics. We find that the
temperature-dependent frequency shift deviates from the Mattis-Bardeen theory,
and the dissipation response shows a shorter decay time than the frequency
response at low temperatures. We suggest that the observed anomalous
electrodynamics may be related to quasiparticle traps or subgap states in the
disordered TiN films. Finally, the electron density-of-states is derived from
the pulse response.Comment: 4 pages, 3 figure
Membrane-Based Scanning Force Microscopy
We report the development of a scanning force microscope based on an ultrasensitive silicon nitride membrane optomechanical transducer. Our development is made possible by inverting the standard microscope geometry - in our instrument, the substrate is vibrating and the scanning tip is at rest. We present topography images of samples placed on the membrane surface. Our measurements demonstrate that the membrane retains an excellent force sensitivity when loaded with samples and in the presence of a scanning tip. We discuss the prospects and limitations of our instrument as a quantum-limited force sensor and imaging tool.</p
- …