5,878 research outputs found
Pattern Formation on Trees
Networks having the geometry and the connectivity of trees are considered as
the spatial support of spatiotemporal dynamical processes. A tree is
characterized by two parameters: its ramification and its depth. The local
dynamics at the nodes of a tree is described by a nonlinear map, given rise to
a coupled map lattice system. The coupling is expressed by a matrix whose
eigenvectors constitute a basis on which spatial patterns on trees can be
expressed by linear combination. The spectrum of eigenvalues of the coupling
matrix exhibit a nonuniform distribution which manifest itself in the
bifurcation structure of the spatially synchronized modes. These models may
describe reaction-diffusion processes and several other phenomena occurring on
heterogeneous media with hierarchical structure.Comment: Submitted to Phys. Rev. E, 15 pages, 9 fig
Comparison of two co-located Infantry Battalions during the 1918 influenza pandemic with very different mortality experiences
The 1918-1919 influenza pandemic was the greatest mortality event in recent history whose specific origins and mechanism remain largely unexplained. Wide ranges of mortality were observed in otherwise identical groups for unclear reasons. The 49th (n=1363) and 50th (n=1243) Battalions (BN) of the Australian Imperial Force (AIF) respectively had one of the highest and lowest influenza mortality rates of any Australian infantry unit. All non-combat mortality, specific pneumonia/influenza mortality and morbidity due to influenza-like illness were collected from both battalions 1916-1919. Mortality during the 1916-1917 epidemic of 'purulent bronchitis' was similar (8 deaths in both) whereas the 49th BN had 18 and the 50th BN had one pneumonia deaths during the influenza pandemic of late 1918-early 1919. Influenza morbidity was similar in both units except during mid-1918 when the 50th BN experienced more cases of a mild influenza-like illness (69 vs 103 cases in June). The 49th BN had more recorded cases of influenza than the 50th BN during the late 1918 pandemic (116 vs 62 cases in October). Recent influenza-like illness appeared to markedly decrease influenza mortality without greatly changing influenza morbidity in 1918
Alternative Sources of Large Seasonal Ground-water Supplies in the Headwaters of the Susquehanna River Basin, New York
The northern divide of the Susquehanna River basin crosses 29 broad valleys that contain thick glacial deposits but are drained only by small headwater streams. Much groundwater could be withdrawn from sand and gravel deposits in these valleys with little immediate effect on streamflow. A digital model of the headwater reach of one typical valley suggests that pumping 10.8 million gal/day for 2 months every summer would lower the water table as much as 33 ft, cause the upper 1,900 ft of the stream draining the valley to go dry, and reduce streamflow downvalley by 1.2 million gal/day by the time pumping ceased. Saturated thickness of surficial sand and gravel exceeds 40 ft in about half the headwater valley reaches; the valley floor areas range from 0.2 to 9 sq mi. Seepage losses from small streams that carry runoff from adjacent till-covered uplands are a major source of recharge to aquifers in these valleys under natural conditions and would increase if the water table were lowered by seasonal withdrawals. Some aquifers beneath extensive clay layers in these and other valleys of the Susquehanna River basin may be partially independent of streams but not easily evaluated. (USGS
Cyclotron effect on coherent spin precession of two-dimensional electrons
We investigate the spin dynamics of high-mobility two-dimensional electrons
in GaAs/AlGaAs quantum wells grown along the and directions by
time-resolved Faraday rotation at low temperatures. In measurements on the
-grown structures without external magnetic fields, we observe coherent
oscillations of the electron spin polarization about the effective spin-orbit
field. In non-quantizing magnetic fields applied normal to the sample plane,
the cyclotron motion of the electrons rotates the effective spin-orbit field.
This rotation leads to fast oscillations in the spin polarization about a
non-zero value and a strong increase in the spin dephasing time in our
experiments. These two effects are absent in the -grown structure due to
the different symmetry of its effective spin-orbit field. The measurements are
in excellent agreement with our theoretical model.Comment: 4 pages, 3 figure
Estimating Soil Moisture Under Low Frequency Surface Irrigation Using Crop Water Stress Index
The present study investigated the relationship between the crop water stress index (CWSI) and soil moisture for surface irrigated cotton (Gossypium hirsutum, Delta Pine 90b) at Maricopa, Arizona during the 1998 season. The CWSI was linked to soil moisture through the water stress coefficient Ks that accounts for reduced crop evapotranspiration when there is a shortage of soil water. A stress recovery coefficient Krec was introduced to account for reduced crop evapotranspiration as the crop recovered from water stress after irrigation events. A soil water stress index (SWSI) was derived in terms of Ks and Krec . The SWSI compared reasonably well to the CWSI, but atmospheric stability correction for the CWSI did not improve comparisons. When the CWSI was substituted into the SWSI formulation, it gave good prediction of soil moisture depletion (fDEP; when to irrigate) and depth of root zone depletion (Dr ; how much to irrigate). Disagreement was greatest for fDEP\u3c0.6 because cotton is less sensitive to water stress in this range
New way to achieve chaotic synchronization in spatially extended systems
We study the spatio-temporal behavior of simple coupled map lattices with
periodic boundary conditions. The local dynamics is governed by two maps,
namely, the sine circle map and the logistic map respectively. It is found that
even though the spatial behavior is irregular for the regularly coupled
(nearest neighbor coupling) system, the spatially synchronized (chaotic
synchronization) as well as periodic solution may be obtained by the
introduction of three long range couplings at the cost of three nearest
neighbor couplings.Comment: 5 pages (revtex), 7 figures (eps, included
Gravitational lensing: a unique probe of dark matter and dark energy
I review the development of gravitational lensing as a powerful tool of the observational cosmologist. After the historic eclipse expedition organized by Arthur Eddington and Frank Dyson, the subject lay observationally dormant for 60 years. However, subsequent progress has been astonishingly rapid, especially in the past decade, so that gravitational lensing now holds the key to unravelling the two most profound mysteries of our Universeâthe nature and distribution of dark matter, and the origin of the puzzling cosmic acceleration first identified in the late 1990s. In this non-specialist review, I focus on the unusual history and achievements of gravitational lensing and its future observational prospects
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Childhood abuse and eating psychopathology: the mediating role of core beliefs
This study aimed to investigate the mediating role of early maladaptive schemas (core beliefs) in the relationship between childhood abuse and eating psychopathology. Three self-report questionnaires assessing experiences of childhood abuse, eating psychopathology, and levels of maladaptive schemas were administered to 118 female university students. Emotional abuse predicted drive for thinness, whereas sexual abuse predicted symptoms of bulimia nervosa (BN). Mistrust and abuse beliefs were found to fully mediate relationships between childhood abuse and drive for thinness and bulimia scales. Abandonment beliefs were also shown to be partial mediators of the relationship between sexual abuse and symptoms of BN. In a sample of nonclinical women, beliefs pertaining to abandonment and mistrust or abuse appeared to be important in the explanation of the relationship between recollections of childhood abuse and adult eating disorder symptoms
Seeding Techniques for Alfalfa to Improve Subirrigated Meadows
Improving quality and quantity of forage harvested from poor condition, subirrigated hay meadows in the Nebraska Sand Hills is critical to the winter forage reserve of livestock producers. Alfalfa (Medicago sativa L.) is the most commonly used legume for meadow improvement. Broadcast seeding (11.2 kg/ha) was compared to sod seeding (11.2 kg/ha) as a method to introduce alfalfa into an alkaline subirrigated meadow (Fluvaquentic Haplustolls). Before seeding, the study area received 78.5 kg/ha phosphorous. Paraquat (0.29 kg/ha) was applied to one-half of the area to suppress plant competition and provide qualitative information on treatment consistency across a range of sod competition. Lo-till sod seeding was accomplished with a power tillage seeder. Seedling density was determined in spring the following year. Broadcast alfalfa had a greater seedling density than sod-seeded alfalfa (38.4 and 19.1 plants/m2, respectively, p=.09). Apparently, paraquat had no effect on seedling establishment and tended to reduce total yield. Yields the year of seeding, using a two harvest scheme, were greater for broadcast compared to sod-seeded alfalfa (p=.02). However, there was no significant difference between yields of broadcast alfalfa and control
Detection of abandoned mineshafts using towed-array capacitive resistivity and real-time kinematic GPS navigation
The UK has a long history of mining but it was not until 1875 that the accurate mapping of mine workings and the submission of abandonment plans became a legal requirement. Where mineshafts are indicated on plans, they may be mislocated due to poor or inaccurate surveying. Consequently, the redevelopment of derelict land in the built environment frequently encounters potential geohazards, such as old adits, bell pits and shafts. These mining relics pose a serious risk to health and safety.
This paper demonstrates how the combination of modem geophysical survey techniques with state-of-the-art satellite-based positioning may assist in the detection of such features. Recent advances in these fields offer the possibility of using towed-array resistivity instruments in conjunction with highly accurate (sub-decimetre) real-time kinematic global positioning systems (RTKGPS). Here we describe the use of multi-offset towed-array capacitive resistivity (CR) with GPS navigation for mapping resistivity over a known mineshaft in the historic mining area of Bonsall Leys in Derbyshire, UK
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