共查询到20条相似文献,搜索用时 9 毫秒
1.
2.
Nanotechnology, as with many technologies before it, places a strain on existing legislation and poses a challenge to all
administrative agencies tasked with regulating technology-based products. It is easy to see how statutory schemes become outdated,
as our ability to understand and affect the world progresses. In this article, we address the regulatory problems that nanotechnology
posses for the Food and Drug Administration’s (FDA) classification structure for “drugs” and “devices.” The last major modification
to these terms was in 1976, with the enactment of the Medical Device Amendments. There are serious practical differences for
a classification as a drug or device in terms of time to market and research. Drugs are classified, primarily, as acting by
“chemical action.” We lay out some legal, philosophic, and scientific tools that serve to provide a useful, as well as legally
and scientifically faithful, distinction between drugs and devices for the purpose of regulatory classification. These issues
we raise are worth the consideration of anyone who is interested in the regulation of nano-products or other novel technologies. 相似文献
3.
4.
Leo P. Kadanoff 《Journal of statistical physics》2009,137(5-6):777-797
This paper is the first in a series that will look at the theory of phase transitions from the perspectives of physics and the philosophy of science. The series will consider a group of related concepts derived from condensed matter and statistical physics. The key technical ideas go under the names of “singularity”, “order parameter”, “mean field theory”, “variational method”, “correlation length”, “universality class”, “scale changes”, and “renormalization”. The first four of these will be considered here. In a less technical vein, the question here is how can matter, ordinary matter, support a diversity of forms. We see this diversity each time we observe ice in contact with liquid water or see water vapor (steam) come up from a pot of heated water. Different phases can be qualitatively different in that walking on ice is well within human capacity, but walking on liquid water is proverbially forbidden to ordinary humans. These differences have been apparent to humankind for millennia, but only brought within the domain of scientific understanding since the 1880s. A phase transition is a change from one behavior to another. A first order phase transition involves a discontinuous jump in some statistical variable. The discontinuous property is called the order parameter. Each phase transition has its own order parameter. The possible order parameters range over a tremendous variety of physical properties. These properties include the density of a liquid-gas transition, the magnetization in a ferromagnet, the size of a connected cluster in a percolation transition, and a condensate wave function in a superfluid or superconductor. A continuous transition occurs when the discontinuity in the jump approaches zero. This article is about statistical mechanics and the development of mean field theory as a basis for a partial understanding of phase transition phenomena. Much of the material in this review was first prepared for the Royal Netherlands Academy of Arts and Sciences in 2006. It has appeared in draft form on the authors’ web site (http://jfi.uchicago.edu/~leop/) since then. The title of this article is a hommage to Philip Anderson and his essay “More is Different” (Sci. New Ser. 177(4047):393–396, 1972; N.-P. Ong and R. Bhatt (eds.) More is Different: Fifty Years of Condensed Matter Physics, Princeton Series in Physics, Princeton University Press, 2001) which describes how new concepts, not applicable in ordinary classical or quantum mechanics, can arise from the consideration of aggregates of large numbers of particles. Since phase transitions only occur in systems with an infinite number of degrees of freedom, such transitions are a prime example of Anderson’s thesis. 相似文献
5.
6.
采用Monte Carlo模拟方法研究了多嵌段聚合物在A/B/嵌段聚合物三组份体系作为相容剂使用的有效性.占总体积19%的A组份在体系中为分散相.模拟结果显示了两嵌段和多嵌段聚合物在界面上的聚集行为,以及如何影响这个不相容体系的相形为.两嵌段聚合物趋于直立在相界面上,而多嵌段聚合物更容易横跨在相界面上并占据较大的界面积.从而导致多嵌段聚合物更有效的阻止体系相分离的发生. 相似文献
7.
It is argued, that nuclear multineutrons, if they exist at all, are rather heavy nuclei, which contain at least 100 neutrons. 相似文献
8.
Konstantinos Dimopoulos 《Contemporary Physics》2013,54(6):633-646
The fundamental paradox of the incompatibility of the observed large-scale uniformity of the Universe with the fact that the age of the Universe is finite is overcome by the introduction of an initial period of superluminal expansion of space, called cosmic inflation. Inflation can also produce the small deviations from uniformity needed for the formation of structures in the Universe such as galaxies. This is achieved by the conjunction of inflation with the quantum vacuum, through the so-called particle production process. This mechanism is explained and linked with Hawking radiation of black holes. The nature of the particles involved is discussed and the case of using massive vector boson fields instead of scalar fields is presented, with emphasis on its distinct observational signatures. Finally, a particular implementation of these ideas is included, which can link the formation of galaxies, the standard model vector bosons and the observed galactic magnetic fields. 相似文献
9.
The ill-posed linear inverse problems, characterised by Fredholm integral equations of the first kind, are encountered in
many areas of science and technology. This type of problems present some loss of information under the inversion process.
The loss of information often makes the inversion process very difficult. Magnetic force microscopy (MFM) is a technique where
problems related to loss of information occur. Work is presented here to understand what can be measured by the magnetic force
microscope. A simple model is constructed, where the magnetic tip is approximated by a point dipole. Given the force F() acting on the dipole tip, we attempt to determine the magnetization distributlon in a thin ferromagnetic film, M(). This calculation should be interesting due to the rapidiy growing interest in magnetic thin films and magnetic multilayers.
Received 3 December 2001 and Received in final form 11 March 2002 相似文献
10.
The aim of this paper is to clarify the conceptual difference which
exists between the interactions of composite bosons and the interactions
of elementary bosons. A special focus is made on the physical processes
which are missed when composite bosons are replaced by elementary bosons.
Although what is here said directly applies to excitons, it is also valid
for composite bosons in other fields than semiconductor physics. We, in
particular, explain how the two elementary scatterings – Coulomb and
Pauli – of our many-body theory for composite excitons, can be extended
to a pair of fermions which is not an Hamiltonian eigenstate – as for
example a pair of trapped electrons, of current interest in quantum
information. 相似文献
11.
C. B. Collins 《Communications in Mathematical Physics》1971,23(2):137-158
Standard geometric techniques of differential equation theory are employed to determine the qualitative behaviour of a set of non-rotating perfect-fluid cosmologies, whose spatially homogeneous hypersurfaces admit a 3-parameter group of isometries of Bianchi types I, II, III, V, or VI. In this way we are led to some new exact solutions of the field equations.The field equations for a broad class of cosmological models are presented in a regularised form, limitations on the use of this procedure are examined, and some suggestions are made of ways of avoiding the difficulties that arise. 相似文献
12.
We propose a supersymmetric model of particle physics in which supersymmetry is broken by strong gauge forces. Unlike previous realistic supersymmetric technicolor theories, the model contains only one extra strong gauge group, and it lends itself readily to grand unification. The model also has no light axions which can burn out stars. A variety of new particles, many weighing less than 100 GeV, are predicted. A no-go theorem due to Witten is discussed. 相似文献
13.
D. Lorenz-Petzold 《Physics letters. [Part B]》1985,158(2):110-114
We present new non-trivial cosmological d=11 supergravity Friedmann-Robertson-Walker-Bianchi solutions with a time-dependent cosmological term. 相似文献
14.
16.
17.
We consider features of experimental studies performed by microwave spectroscopy methods and showing the collisional pressure
broadening of molecular lines by hydrogen at very low temperatures. It is shown that the effect of preferential adsorption
of orthohydrogen by the walls of the gas cell of a spectrometer can influence significantly the measurement results and lead
to an erroneous interpretation of the data given by astrophysical studies of the interstellar space. 相似文献
18.
19.
An analysis of experimental data available to the date and concerning the dependence of projectile fragments (PFs) mean free path (mfp) in heavy-ion collisions on the distance from the point of their emission is presented. The linear dependence of the relative variation of the estimates of the mfp on 1/N, whereN is the number of PFs observed, has been established. This dependence seems to be understood only from the statistical point of view. It has been shown that the idea of the absence of anomalons in the Nature does not contradict the data of 27 experimental works out of 29 considered. 相似文献
20.
A. S. Barabash 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):137-140
A comparison is made of the probability of the process of two neutrino double-beta decay for 82Se and 96Zr in direct (counter) and geochemical experiments. The experimental data for 130Te are also analyzed. It is shown that the probability is systematically lower in geochemical experiments, which characterize
the probability of decay a few billions years ago. In addition geochemical measurements on young minerals give lower values of T
(130Te) as compared to measurements on old minerals. It is proposed that this could be due to a change in the weak interaction
constant with time. The possibilities of new precise measurements to be performed with the aid of counters and geochemical
experiments are discussed. A new geochemical experiment with 100Mo is proposed.
Received: 24 February 2000 / Accepted: 4 March 2000 相似文献