17,501 research outputs found
Rigorous bounds on the effective moduli of composites and inhomogeneous bodies with negative-stiffness phases
We review the theoretical bounds on the effective properties of linear
elastic inhomogeneous solids (including composite materials) in the presence of
constituents having non-positive-definite elastic moduli (so-called
negative-stiffness phases). We show that for statically stable bodies the
classical displacement-based variational principles for Dirichlet and Neumann
boundary problems hold but that the dual variational principle for traction
boundary problems does not apply. We illustrate our findings by the example of
a coated spherical inclusion whose stability conditions are obtained from the
variational principles. We further show that the classical Voigt upper bound on
the linear elastic moduli in multi-phase inhomogeneous bodies and composites
applies and that it imposes a stability condition: overall stability requires
that the effective moduli do not surpass the Voigt upper bound. This
particularly implies that, while the geometric constraints among constituents
in a composite can stabilize negative-stiffness phases, the stabilization is
insufficient to allow for extreme overall static elastic moduli (exceeding
those of the constituents). Stronger bounds on the effective elastic moduli of
isotropic composites can be obtained from the Hashin-Shtrikman variational
inequalities, which are also shown to hold in the presence of negative
stiffness
Prospectives in Deep Space Infrastructures, Development, and Colonization
The realization of the long studied cost reduction benefits of reusable rockets is expected to revolutionize and enable both commercial deep space beyond Geostationary Earth Orbit (GEO) and solar system human colonization. The projections for a myriad of space commercialization activities beyond the current largely positional Earth utilities and Humans Mars both safe and affordable may now be realizable. This report considers these putative commercial and colonizationrelated activities, the emerging technologies, the space functionalities to support and further enable them, and envisions the nature of space developments beyond GEO going forward
Hematology as Related to Diving Characteristics of Elaphe obsoleta, Nerodia erythrogaster, Nerodia Fasciata and Nerodia rhombifera
The diving capabilities of Nerodia erythrogaster flavigaster and Nerodia fasciata confluens were investigated and the results were compared with similar studies on Nerodia rhombifera rhombifera and Elaphe obsoleta obsoleta (Baeyens et al., 1978). In addition, morphological and hematological parameters contributing to underwater survival were examined. The duration of underwater survival for N. erythrogaster and N. fasciata was approximately one hour with no difference between the species. The lung volumes of the two species were also similar but were significantly less than lung volumes reported for E. obsoleta. There were no significant differences in hemoglobin concentration, red blood cell count or hematocrit between N. rhombifera, N. erythrogaster, N. fasciata, and E. obsoleta. Based on similarities in underwater tolerance, lung morphology and hematology, Nerodia more closely resembles the terrestrial E. obsoleta than those reptiles specifically adapted to an underwater existance
Differential thermal analysis and solution growth of intermetallic compounds
To obtain single crystals by solution growth, an exposed primary
solidification surface in the appropriate, but often unknown, equilibrium alloy
phase diagram is required. Furthermore, an appropriate crucible material is
needed, necessary to hold the molten alloy during growth, without being
attacked by it. Recently, we have used the comparison of realistic simulations
with experimental differential thermal analysis (DTA) curves to address both
these problems. We have found: 1) complex DTA curves can be interpreted to
determine an appropriate heat treatment and starting composition for solution
growth, without having to determine the underlying phase diagrams in detail. 2)
DTA can facilitate identification of appropriate crucible materials. DTA can
thus be used to make the procedure to obtain single crystals of a desired phase
by solution growth more efficient. We will use some of the systems for which we
have recently obtained single-crystalline samples using the combination of DTA
and solution growth as examples. These systems are TbAl, PrNiSi,
and YMnAl.Comment: 17 pages, 8 figure
A taxonomic guide to the mysids of the South Atlantic Bight.
Following the examination of extensive collections from the National Museum of Natural History (NMNH), the Southeastern Regional Taxonomic Center (SERTC), and other regional institutions, 18 species of the family Mysidae are recognized and described from the South Atlantic Bight
(Cape Lookout, North Carolina to Cape Canaveral, Florida). This report includes synonymies of previous records, as well as new species distribution records. Previous
regional accounts of Metamysidopsis munda and Metamysidopsis mexicana are attributed to Metamysidopsis swifti. New regional records are established for Amathimysis brattegardi, Heteromysis beetoni, and Siriella thompsonii. Two other species tentatively identified as
Amathimysis sp. (nr. serrata) and Mysidopsis sp. (cf. mortenseni) may represent new taxa. Neobathymysis renoculata is included and discussed as a potential regional species. An illustrated key to the species currently known from the South Atlantic Bight is presented.
Relevant taxonomic, distributional, and ecological information is also included for each species. (PDF file contains 45 pages.
Law-Based Arguments and Messages to Advocate for Later School Start Time Policies in the United States
The increasing scientific evidence that early school start times are harmful to the health and safety of teenagers has generated much recent debate about changing school start times policies for adolescent students. Although efforts to promote and implement such changes have proliferated in the United States in recent years, they have rarely been supported by law-based arguments and messages that leverage the existing legal infrastructure regulating public education and child welfare in the United States. Furthermore, the legal bases to support or resist such changes have not been explored in detail to date. This article provides an overview of how law-based arguments and messages can be constructed and applied to advocate for later school start time policies in U.S. public secondary schools. The legal infrastructure impacting school start time policies in the United States is briefly reviewed, including descriptions of how government regulates education, what legal obligations school officials have concerning their students\u27 welfare, and what laws and public policies currently exist that address adolescent sleep health and safety. On the basis of this legal infrastructure, some hypothetical examples of law-based arguments and messages that could be applied to various types of advocacy activities (e.g., litigation, legislative and administrative advocacy, media and public outreach) to promote later school start times are discussed. Particular consideration is given to hypothetical arguments and messages aimed at emphasizing the consistency of later school start time policies with existing child welfare law and practices, legal responsibilities of school officials and governmental authorities, and societal values and norms
Reconstructing Positions \& Peculiar Velocities of Galaxy Clusters within 25000 km/sec: The Bulk Velocity
Using a dynamical 3-D reconstruction procedure we estimate the peculiar
velocities of Abell/ACO galaxy clusters from their measured redshift
within 25000 km/sec. The reconstruction algorithm relies on the linear
gravitational instability hypothesis, assumes linear biasing and requires an
input value of the cluster -parameter (), which we estimated in Branchini \& Plionis (1995)
to be . The resulting cluster velocity field is dominated
by a large scale streaming motion along the Perseus Pisces--Great Attractor
base-line directed towards the Shapley concentration, in qualitative agreement
with the galaxy velocity field on smaller scales. Fitting the predicted cluster
peculiar velocities to a dipole term, in the local group frame and within a
distance of km/sec, we recover extremely well both the local group
velocity and direction, in disagreement with the Lauer \& Postman (1994)
observation. However, we find a probability that their observed
velocity field could be a realization of our corresponding one, if the latter
is convolved with their large distance dependent errors. Our predicted cluster
bulk velocity amplitude agrees well with that deduced by the POTENT and the da
Costa et al. (1995) analyses of observed galaxy motions at
km/sec; it decreases thereafter while at the Lauer \& Postman limiting depth
( km/sec) its amplitude is km/sec, in comfortable
agreement with most cosmological models.Comment: 8 pages, uuencoded compressed tarred postscript file uncluding text
and 3 figures. Accepted in ApJ Letter
Parameter identification for an abstract Cauchy problem by quasilinearization
A parameter identification problem is considered in the context of a linear abstract Cauchy problem with a parameter-dependent evolution operator. Conditions are investigated under which the gradient of the state with respect to a parameter possesses smoothness properties which lead to local convergence of an estimation algorithm based on quasi-linearization. Numerical results are presented concerning estimation of unknown parameters in delay-differential equations
How Well Does "Core" CPI Capture Permanent Price Changes?
We decompose core CPI and the food and energy CPI measures into permanent and transitory components using a correlated unobserved components model, to examine the behavior of core CPI when subject to shocks and to examine the claim that core CPI captures the persistent part of headline CPI. We find that the permanent component of core CPI is more volatile than core CPI, or that the permanent and transitory components are highly correlated. We find that the excluded food and energy components have important permanent components, and that core CPI has an important transitory component. We examine impulse response functions and find that headline CPI inflation responds more sharply to shocks than core CPI inflation, and after the first year the impact of shocks on headline inflation is less than the impact on core inflation.unobserved components, CPI, price indices, inflation, core
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