共查询到20条相似文献,搜索用时 32 毫秒
1.
G Baskaran 《Pramana》2002,58(2):427-437
A few billion years of evolutionary time and the complex process of ‘selection’ has given biology an opportunity to explore
a variety of condensed matter phenomena and situations, some of which have been discovered by humans in the laboratory, that
too only in extreme non-biological conditions such as low temperatures, high purity, high pressure etc., in the last centuries.
Biology, at some level, is a complex and self-regulated condensed matter system compared to the ‘inanimate’ condensed matter
systems such as liquid 4He, liquid water or a piece of graphite. In this article I propose a hypothesis that ‘all basic condensed matter physics phenomena
and notions (already known and ones yet to be discovered) mirror in biology’. I explain this hypothesis by considering the
idea of ‘Bose condensation’ or ‘momentum space order’ and discuss two known example of quantum magnetism encountered in biology.
I also provide some new and rather speculative possibility, from light harvesting in biological photosynthesis, of mesoscopic
excition condensation related phenomena at room temperature. 相似文献
2.
The phenomenon of quantum superposition, which allows a physical system to exist in different states ‘simultaneously’, is
one of the most bizarre notions in physics. Here we illustrate an even more bizarre example of it: a superposed state of a
physical system consisting of both an ‘older’ version and a ‘younger’ version of that system. This can be accomplished by
exploiting the special relativistic effect of time dilation featuring in Einstein’s famous twin paradox. 相似文献
3.
Summary The data for 3.8 million compounds from structural databases of 32 providers were gathered and stored in a single chemical database. Duplicates are removed using the IUPAC International Chemical Identifier. After this, 2.6 million compounds remain. Each database and the final one were studied in term of uniqueness, diversity, frameworks, ‘drug-like’ and ‘lead–like’ properties. This study also shows that there are more than 87 000 frameworks in the database. It contains 2.1 million ‘drug-like’ molecules among which, more than one million are ‘lead-like’. This study has been carried out using ‘ScreeningAssistant’, a software dedicated to chemical databases management and screening sets generation. Compounds are stored in a MySQL database and all the operations on this database are carried out by Java code. The druglikeness and leadlikeness are estimated with ‘in–house’ scores using functions to estimate convenience to properties; unicity using the InChI code and diversity using molecular frameworks and fingerprints. The software has been conceived in order to facilitate the update of the database. ‘ScreeningAssistant’ is freely available under the GPL license. 相似文献
4.
Simple considerations regarding the Hamiltonian and the ground state wavefunctions of Λ-hypernuclei are used to derive several
mass formulae. The parameters that occur in the mass formulae are determined by fitting the experimental binding energies.
Information regarding the various interactions in hypernuclal is deduced from the values of these parameters. The ‘best’ mass
formula is further used to predict energies of other light hypernuclei. Relationship between binding energies are also suggested
and checked with observed data. 相似文献
5.
6.
Mean velocity data obtained by PIV (Particle Image Velocimetry) around the head of a real-life size breathing thermal manikin
are presented for two cases of ‘no breathing’ and ‘continuous exhalation through nose’. Experiments were conducted in a special
chamber which provided stationary convective flows around the seated manikin. Results are limited to the plane of symmetry.
The paper aims to describe the physical structure of the turbulent flow field by presenting velocity and vorticity data in
color graphics. 相似文献
7.
Travis Norsen 《Foundations of Physics》2007,37(3):311-340
We examine the prevalent use of the phrase “local realism” in the context of Bell’s Theorem and associated experiments, with
a focus on the question: what exactly is the ‘realism’ in ‘local realism’ supposed to mean? Carefully surveying several possible
meanings, we argue that all of them are flawed in one way or another as attempts to point out a second premise (in addition
to locality) on which the Bell inequalities rest, and (hence) which might be rejected in the face of empirical data violating
the inequalities. We thus suggest that the phrase ‘local realism’ should be banned from future discussions of these issues,
and urge physicists to revisit the foundational questions behind Bell’s Theorem. 相似文献
8.
We discuss questions pertaining to the definition of ‘momentum’, ‘momentum space’, ‘phase space’ and ‘Wigner distributions’;
for finite dimensional quantum systems. For such systems, where traditional concepts of ‘momenta’ established for continuum
situations offer little help, we propose a physically reasonable and mathematically tangible definition and use it for the
purpose of setting up Wigner distributions in a purely algebraic manner. It is found that the point of view adopted here is
limited to odd dimensional systems only. The mathematical reasons which force this situation are examined in detail 相似文献
9.
Varun Sahni 《Pramana》2000,55(1-2):43-52
I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation
for invoking a small cosmological constant (or A-term) at the present epoch has to do with observations of high redshift Type
Ia supernovae which suggest an accelerating universe. A flat accelerating universe is strongly favoured by combining supernovae
observations with observations of CMB anisotropies on degree scales which give the ‘best-fit’ values ΘA ⋍ 0.7 and Θ
m
⋍ 0.3. A time dependent cosmological A-term can be generated by scalar field models with exponential and power law potentials.
Some of these models can alleviate the ‘fine tuning’ problem which faces the cosmological constant. 相似文献
10.
Systems driven out of equilibrium can often exhibit behaviour not seen in systems in thermal equilibrium —for example phase
transitions in one-dimensional systems. In this talk I will review a simple model of a nonequilibrium system known as the
‘zero-range process’ and its recent developments. The nonequilibrium stationary state of this model factorises and this property
allows a detailed analysis of several ‘condensation’ transitions wherein a finite fraction of the constituent particles condenses
onto a single lattice site. I will then consider a more general class of mass transport models, encompassing continuous mass
variables and discrete time updating, and present a necessary and sufficient condition for the steady state to factorise.
The property of factorisation again allows an analysis of the condensation transitions which may occur. 相似文献
11.
R. Coisson P.V. Hôi P. Podini B. Huy V.D. Thinh 《Applied physics. B, Lasers and optics》2000,71(6):905-907
‘Low-coherence interferometry’ is an old technique which has had a wide development recently, and is based on the fact that
interference with a path difference much longer that the coherence length gives rise to a ‘channeled spectrum’, which can
be detected either by a dispersive spectroscope or by a second interferometer with a variable delay. We have tested an alternative
way to detect path differences in this kind of interferometry, by analyzing the output intensity fluctuation correlations
by a radiofrequency spectrum analyzer, and Fourier transforming the data. This method is suitable for very long path differences.
The experiments have been performed with different lengths of single-mode fibre, in Mach–Zehnder and Fabry–Pérot configurations.
Received: 30 March 2000 / Revised version: 17 Juli 2000 / Published online: 20 September 2000 相似文献
12.
13.
Tadeusz Wibig 《Pramana》2009,73(5):807-820
The recent claim of the ‘5 sigma’ observation of the Greisen-Zatzepin-Kuzmin cut-off by the HiRes group based on their nine
years data is a significant step towards the eventual solution of one of the most intriguing questions in physics for more
than 40 years. Recent results from Pierre Auger Observatory seem to confirm the statement. However, the word ‘significance’
is used in the mentioned paper in a sense which is not quite obvious. In the present paper we argue that this claim is a little
premature. 相似文献
14.
Proteins are important biomolecules, which perform diverse structural and functional roles in living systems. Starting from
a linear chain of amino acids, proteins fold to different secondary structures, which then fold through short- and long-range
interactions to give rise to the final three-dimensional shapes useful to carry out the biophysical and biochemical functions.
Proteins are defined as having a common ‘fold’ if they have major secondary structural elements with same topological connections.
It is known that folding mechanisms are largely determined by a protein’s topology rather than its interatomic interactions.
The native state protein structures can, thus, be modelled, using a graph-theoretical approach, as coarse-grained networks
of amino acid residues as ‘nodes’ and the inter-residue interactions/contacts as ‘links’. Using the network representation
of protein structures and their 2D contact maps, we have identified the conserved contact patterns (groups of contacts) representing
two typical folds — the EF-hand and the ubiquitin-like folds. Our results suggest that this direct and computationally simple
methodology can be used to infer about the presence of specific folds from the protein’s contact map alone.
相似文献
15.
Sandip Pakvasa 《Pramana》2000,54(1):65-77
I review explanations for the three neutrino anomalies (solar, atmospheric and LSND) which go beyond the ‘conventional’ neutrino
oscillations induced by mass-mixing. Several of these require non-zero neutrino masses as well. 相似文献
16.
Alexander Afriat 《International Journal of Theoretical Physics》2007,46(10):2669-2675
An axiomatic characterization of a ‘two-level Hamiltonian structure’ is proposed, which expresses the optico-mechanical analogy
by representing optics and mechanics as (disjoint) classes of models satisfying the axioms. There is the ‘Hamilton–Jacobi
level’, which involves a differential manifold on which the characteristic function satisfying the Hamilton–Jacobi equation
is defined; and the ‘symplectic level’, involving the Hamiltonian, defined on the cotangent bundle of the manifold. The two
levels, with the (analogous) structures on them, concern both optics and mechanics. 相似文献
17.
Rahul Basu 《Pramana》1998,51(1-2):205-216
In this talk I review the behaviour of structure functions at low values of Bjorkenx and discuss the theoretical underpinnings with particular attention to resummation schemes. I present the need for ‘less
inclusive’ events to distinguish between various resummation schemes and discuss the various difficulties in differentiating
experimentally between different schemes. 相似文献
18.
With the advent of medium and large gamma detector arrays, it is now possible to look at nuclear structure at high rotational
forces. The role of pairing correlations and their eventual breakdown, along with the shell effects have showed us the interesting
physics for nuclei at high spins — superdeformation, shape co-existence, yrast traps, alignments and their dramatic effects
on nuclear structure and so on. Nuclear structure studies have recently become even more exciting, due to efforts and possibilities
to reach nuclei far off from the stability valley. Coupling of gamma ray arrays with ‘filters’, like neutron wall, charged
particle detector array, gamma ray total energy and multiplicity castles, conversion electron spectrometers etc gives a great
handle to study nuclei produced online with ‘low’ cross-sections. Recently we studied, nuclei in mass region 80 using an array
of 8 germanium detectors in conjunction with the recoil mass analyser, HIRA at the Nuclear Science Centre and, most unexpectedly
came across the phenomenon of identical bands, with two quasi-particle difference. The discovery of magnetic rotation is another
highlight. Our study of light In nucleus, 107In brought us face to face with the ‘dipole’ bands. I plan to discuss some of
these aspects. There is also an immensely important development — that of the ‘radioactive ion beams’. The availability of
RIB, will probably very dramatically influence our ‘conventional’ concept of nuclear structure. The exotic shapes of these
exotic nuclei and some of their expected properties will also be touched upon. 相似文献
19.
Wim Christiaens Christian de Ronde Bart D’Hooghe Federico Holik 《International Journal of Theoretical Physics》2010,49(12):3061-3068
In this paper we present Aerts’ vessels of water model which violates Bell inequalities, and discuss how this fits in the
Creation Discovery View in the context of the Operational Quantum Logic approach. We analyze the 2 different ways in which
correlation is classically observed, either as pre-existing ‘independent of measurement’ or established by sending a signal,
hence limited by the speed of light. As the Aerts’ model shows, there is yet a third possibility, namely a situation in which
correlation is potentially present, but only actualized to its full extent by the act of measurement. This creation-discovery
view can be applied to the quantum mechanical situation of two entangled photons, and shows that in the debate of understanding
‘what is really going on in Aspects experiments’ an alternative explanation can be found, in which potentiality, creation
and discovery play a central role. 相似文献
20.
Ruth E. Kastner 《Foundations of Physics》2012,42(8):1094-1113
A recent ontological variant of Cramer’s Transactional Interpretation, called “Possibilist Transactional Interpretation” or
PTI, is extended to the relativistic domain. The present interpretation clarifies the concept of ‘absorption,’ which plays
a crucial role in TI (and in PTI). In particular, in the relativistic domain, coupling amplitudes between fields are interpreted
as amplitudes for the generation of confirmation waves (CW) by a potential absorber in response to offer waves (OW), whereas
in the nonrelativistic context CW are taken as generated with certainty. It is pointed out that solving the measurement problem
requires venturing into the relativistic domain in which emissions and absorptions take place; nonrelativistic quantum mechanics
only applies to quanta considered as ‘already in existence’ (i.e., ‘free quanta’), and therefore cannot fully account for
the phenomenon of measurement, in which quanta are tied to sources and sinks. 相似文献