1,592,421 research outputs found
A physically-based approach for evaluating the hydraulic invariance in urban transformations
Transformation of urban areas satisfies hydraulic invariance (HI) if the maximum flow rate outgoing
the area stays unchanged. The HI can be respected by dimensioning appropriate water storage
volumes or low impact developments (LID) to balance the soil sealing and ground levelling effects.
In order to comply with HI, some Italian regional legislation and river basin authority provide for
the creation of storage tanks whose volume must be estimated through simple conceptual rainfallrunoff
models. In this work a physically based approach for evaluating HI is proposed. It is based on
interpolating the results from a large number of hydraulic simulations conducted using FullSWOF,
which is an open source code developed by the University of Orléans. In this software the shallow
water equations are solved using a finite volume scheme and friction laws and infiltration models
are included. Simulations have been carried out considering the effect of three properties of the
area, that is: the saturated hydraulic conductivity of soil, the slope of ground surface and the standard
deviation of ground elevation around the mean level. Using the results, interpolating laws for
the peak discharge and the critical rainfall duration as function of the three basin parameters have
been derived. A parametric hydrograph as a function of the basin parameters and rainfall duration
is defined and a HI evaluation method based on routing the parametric hydrograph is proposed.
The results from this approach have been compared with those from non-physically based methods
currently used, such as the direct rainfall approach and the linear reservoir approach. The comparison
shows that the difference between these conceptual methods with that one proposed here
is strongly dependent on the runoff coefficient value. It is also not possible to predict whether they
are conservative or not
Physically-Based Modeling
Physically based modeling is a growing trend in computer animation. There are many implementations available for this topic. The most basic of these involves the movement of single particles (without a shape) moving through space. This implementation involves the movement of particles that have a rigid structure, such as a box or ball, known as rigid bodies. It features a simple box comprised of 8 points moving through space according to the laws of physics as it makes contact with a surface
Gamma-ray Bursts, Classified Physically
From Galactic binary sources, to extragalactic magnetized neutron stars, to
long-duration GRBs without associated supernovae, the types of sources we now
believe capable of producing bursts of gamma-rays continues to grow apace. With
this emergent diversity comes the recognition that the traditional (and newly
formulated) high-energy observables used for identifying sub-classes does not
provide an adequate one-to-one mapping to progenitors. The popular
classification of some > 100 sec duration GRBs as ``short bursts'' is not only
an unpalatable retronym and syntactically oxymoronic but highlights the
difficultly of using what was once a purely phenomenological classification to
encode our understanding of the physics that gives rise to the events. Here we
propose a physically based classification scheme designed to coexist with the
phenomenological system already in place and argue for its utility and
necessity.Comment: 6 pages, 3 figures. Slightly expanded version of solicited paper to
be published in the Proceedings of ''Gamma Ray Bursts 2007,'' Santa Fe, New
Mexico, November 5-9. Edited by E. E. Fenimore, M. Galassi, D. Palme
Moisture-triggered physically transient electronics
Physically transient electronics, a form of electronics that can physically disappear in a controllable manner, is very promising for emerging applications. Most of the transient processes reported so far only occur in aqueous solutions or biofluids, offering limited control over the triggering and degradation processes. We report novel moisture-triggered physically transient electronics, which exempt the needs of resorption solutions and can completely disappear within well-controlled time frames. The triggered transient process starts with the hydrolysis of the polyanhydride substrate in the presence of trace amounts of moisture in the air, a process that can generate products of corrosive organic acids to digest various inorganic electronic materials and components. Polyanhydride is the only example of polymer that undergoes surface erosion, a distinct feature that enables stable operation of the functional devices over a predefined time frame. Clear advantages of this novel triggered transience mode include that the lifetime of the devices can be precisely controlled by varying the moisture levels and changing the composition of the polymer substrate. The transience time scale can be tuned from days to weeks. Various transient devices, ranging from passive electronics (such as antenna, resistor, and capacitor) to active electronics ( such as transistor, diodes, optoelectronics, and memories), and an integrated system as a platform demonstration have been developed to illustrate the concept and verify the feasibility of this design strategy
Is Double Reionization Physically Plausible?
Recent observations of z~6 quasars and the cosmic microwave background imply
a complex history to cosmic reionization. Such a history requires some form of
feedback to extend reionization over a long time interval, but the nature of
the feedback and how rapidly it operates remain highly uncertain. Here we focus
on one aspect of this complexity: which physical processes can cause the global
ionized fraction to evolve non-monotonically with cosmic time? We consider a
range of mechanisms and conclude that double reionization is much less likely
than a long, but still monotonic, ionization history. We first examine how
galactic winds affect the transition from metal-free to normal star formation.
Because the transition is actually spatially inhomogeneous and temporally
extended, this mechanism cannot be responsible for double reionization given
plausible parameters for the winds. We next consider photoheating, which causes
the cosmological Jeans mass to increase in ionized regions and hence suppresses
galaxy formation there. In this case, double reionization requires that small
halos form stars efficiently, that the suppression from photoheating is strong
relative to current expectations, and that ionizing photons are preferentially
produced outside of previously ionized regions. Finally, we consider H_2
photodissociation, in which the buildup of a soft ultraviolet background
suppresses star formation in small halos. This can in principle cause the
ionized fraction to temporarily decrease, but only during the earliest stages
of reionization. Finally, we briefly consider the effects of some of these
feedback mechanisms on the topology of reionization.Comment: 13 pages, 5 figures, in press at ApJ (reorganized significantly but
major conclusions unchanged
Physically fit or physically literate? Children with special educational needs understanding of physical education
The role of physical literacy within physical education (PE) has become a widely debated topic in recent years. Its role in educating children about physicality through embodiment, skill acquisition and reading the environment is argued to be of great benefit to children. However, whether children understand the role of PE in the development of these competencies is not clear, and this is even truer for children who have special educational needs (SEN). Drawing on qualitative phenomenological data from 30 children in key stages 2 and three (7 to 14 years of age) who have SEN, this paper explores notions of physical fitness and physical literacy as understood by children in PE lessons. It aims to gain insight into the ways that children understand the purpose of PE, and places these perceptions within a physical literacy framework, using the National Curriculum for PE (NCPE) as a foundation. Findings demonstrate that children with SEN perceive PE as a means for improving physical fitness, whereas concepts surrounding physical literacy appear to be lost. The paper concludes by making recommendations for factoring physical literacy components more forcibly into the PE curriculum, and through initial teacher training and continued professional development
Physically valid black-hole interior models
New, simple models of ``black hole interiors'', namely spherically symmetric
solutions of the Einstein field equations in matter matching the Schwarzschild
vacuum at spacelike hypersurfaces ``R<2M'' are constructed. The models satisfy
the weak energy condition and their matter content is specified by an equation
of state of the elastic type.Comment: 6 pages, TeX forma
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