1,935 research outputs found
Scaling law in target-hunting processes
We study the hunting process for a target, in which the hunter tracks the
goal by smelling odors it emits. The odor intensity is supposed to decrease
with the distance it diffuses. The Monte Carlo experiment is carried out on a
2-dimensional square lattice. Having no idea of the location of the target, the
hunter determines its moves only by random attempts in each direction. By
sorting the searching time in each simulation and introducing a variable to
reflect the sequence of searching time, we obtain a curve with a wide plateau,
indicating a most probable time of successfully finding out the target. The
simulations reveal a scaling law for the searching time versus the distance to
the position of the target. The scaling exponent depends on the sensitivity of
the hunter. Our model may be a prototype in studying such the searching
processes as various foods-foraging behavior of the wild animals.Comment: 7 figure
Modeling the adoption and use of social media by nonprofit organizations
This study examines what drives organizational adoption and use of social
media through a model built around four key factors - strategy, capacity,
governance, and environment. Using Twitter, Facebook, and other data on 100
large US nonprofit organizations, the model is employed to examine the
determinants of three key facets of social media utilization: 1) adoption, 2)
frequency of use, and 3) dialogue. We find that organizational strategies,
capacities, governance features, and external pressures all play a part in
these social media adoption and utilization outcomes. Through its integrated,
multi-disciplinary theoretical perspective, this study thus helps foster
understanding of which types of organizations are able and willing to adopt and
juggle multiple social media accounts, to use those accounts to communicate
more frequently with their external publics, and to build relationships with
those publics through the sending of dialogic messages.Comment: Seungahn Nah and Gregory D. Saxton. (in press). Modeling the adoption
and use of social media by nonprofit organizations. New Media & Society,
forthcomin
AN IRRIGATION MODEL FOR MANAGEMENT OF LIMITED WATER SUPPLIES
A two-stage simulation/mathematical programming model is presented for determining the optimal intraseasonal allocation of irrigation water under conditions of limited water supply. The model is applied to a series of water shortage scenarios under both surface and center pivot irrigation. Economically efficient irrigation management is shown to involve the coordination of a number of managerial decisions, including irrigation scheduling, crop substitution, the adoption of improved irrigation labor practices, and idling land. The results indicate that significant opportunities exist for conserving water in the study area under both surface and center pivot irrigation.Crop Production/Industries, Resource /Energy Economics and Policy,
Oxygen isotopes implanted in the LDEF spacecraft
Secondary ion mass spectrometry was used to study oxygen implanted in the surface of copper from the Long Duration Exposure Facility (LDEF). Oxidation that occurred in orbit shows a characteristic oxygen isotope composition, depleted in O-18. The measured depletion is comparable to the predicted depletion (45 percent) based on a model of the gravitational separation of the oxygen isotopes. The anomalous oxygen was contained within 10nm of the surface. Tray E10 was calculated to have received 5.14 x 10(exp 21) atoms of oxygen cm(sup -2) during the LDEF mission and so there is sufficient anomalous implanted oxygen present in the surface to obtain a reliable isotopic profile
The Dynamics of Radiative Shock Waves: Linear and Nonlinear Evolution
The stability properties of one-dimensional radiative shocks with a power-law
cooling function of the form are the main
subject of this work. The linear analysis originally presented by Chevalier &
Imamura, is thoroughfully reviewed for several values of the cooling index
and higher overtone modes. Consistently with previous results, it is
shown that the spectrum of the linear operator consists in a series of modes
with increasing oscillation frequency. For each mode a critical value of the
cooling index, , can be defined so that modes with are unstable, while modes with
are stable. The perturbative analysis is complemented by several numerical
simulations to follow the time-dependent evolution of the system for different
values of . Particular attention is given to the comparison between
numerical and analytical results (during the early phases of the evolution) and
to the role played by different boundary conditions. It is shown that an
appropriate treatment of the lower boundary yields results that closely follow
the predicted linear behavior. During the nonlinear regime, the shock
oscillations saturate at a finite amplitude and tend to a quasi-periodic cycle.
The modes of oscillations during this phase do not necessarily coincide with
those predicted by linear theory, but may be accounted for by mode-mode
coupling.Comment: 33 pages, 12 figures, accepted for publication on the Astrophysical
Journa
Rapid late-time X-ray brightening of the tidal disruption event OGLE16aaa
Stars that pass too close to a super-massive black hole may be disrupted by
strong tidal forces. OGLE16aaa is one such tidal disruption event (TDE) which
rapidly brightened and peaked in the optical/UV bands in early 2016 and
subsequently decayed over the rest of the year. OGLE16aaa was detected in an
XMM-Newton X-ray observation on June 9, 2016 with a flux slightly below the
Swift/XRT upper limits obtained during the optical light curve peak. Between
June 16-21, 2016, Swift/XRT also detected OGLE16aaa and based on the stacked
spectrum, we could infer that the X-ray luminosity had jumped up by more than a
factor of ten in just one week. No brightening signal was seen in the
simultaneous optical/UV data to cause the X-ray luminosity to exceed the
optical/UV one. A further XMM-Newton observation on November 30, 2016 showed
that almost a year after the optical/UV peak, the X-ray emission was still at
an elevated level, while the optical/UV flux decay had already leveled off to
values comparable to those of the host galaxy. In all X-ray observations, the
spectra were nicely modeled with a 50-70 eV thermal component with no intrinsic
absorption, with a weak X-ray tail seen only in the November 30 XMM-Newton
observation. The late-time X-ray behavior of OGLE16aaa strongly resembles the
tidal disruption events ASASSN-15oi and AT2019azh. We were able to pinpoint the
time delay between the initial optical TDE onset and the X-ray brightening to
days, which may possibly represent the timescale between the
initial circularization of the disrupted star around the super-massive black
hole and the subsequent delayed accretion. Alternatively, the delayed X-ray
brightening could be related to a rapid clearing of a thick envelope that
covers the central X-ray engine during the first six months.Comment: 8 pages, 2 figures, Accepted for publication in A&
Use of soil moisture information in yield models
There are no author-identified significant results in this report
Effects of an exercise and hypocaloric healthy eating intervention on indices of psychological health status, hypothalamic-pituitary-adrenal axis regulation and immune function after early-stage breast cancer : a randomised controlled trial
INTRODUCTION: Many women experience emotional distress, depression and anxiety after a diagnosis of breast cancer. Psychological stress and depression have been associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation that may adversely affect immune system functioning and impact upon survival. This study investigated the effects of a lifestyle intervention on indices of psychological health status, HPA axis regulation and immune function in overweight women recovering from early-stage breast cancer treatment.
METHODS: A total of 85 women treated for breast cancer 3 to 18 months previously were randomly allocated to a 6-month exercise and hypocaloric healthy eating program plus usual care or usual care alone (control group). Women in the intervention group received three supervised exercise sessions per week and individualized dietary advice, supplemented by weekly nutrition seminars. Depressive symptoms (Beck Depression Inventory version II: BDI-II), perceived stress (Perceived Stress Scale: PSS), salivary diurnal cortisol rhythms; inflammatory cytokines (IL-6 and Tumor necrosis factor-α), leukocyte phenotype counts, natural killer (NK) cell cytotoxicity and lymphocyte proliferation following mitogenic stimulation were assessed at baseline and 6-month follow up. RESULTS: Compared with the control group, the intervention group exhibited a reduction in depressive symptoms (adjusted mean difference, 95% confidence intervals (95% CI): -3.12, -1.03 to -5.26; P = 0.004) at the 6-month follow-up but no significant decrease in PSS scores (-2.07, -4.96 to 0.82; P = 0.16). The lifestyle intervention also had a significant impact on diurnal salivary cortisol rhythm compared with usual care alone, as evidenced by an increase in morning salivary cortisol at the 6-month follow-up (P <0.04), indicating a change in HPA axis regulation. Women in the control group had higher total leukocyte, neutrophil and lymphocyte counts in comparison to the intervention group at the 6-month follow-up (P ≤0.05), whereas there was no difference in NK cell counts (P = 0.46), NK cell cytotoxicity (P = 0.85) or lymphocyte proliferation responses (P = 0.11) between the two groups. CONCLUSION: Our results show that the lifestyle intervention resulted in a reduction in depressive symptoms and a normalisation of HPA axis regulation. Such changes could have important implications for long-term survival in women recovering from early-breast cancer treatment. TRIAL REGISTRATION: Current Controlled Trials: ISRCTN08045231
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