Messanae Universitas Studiorum: No conditions. Results ordered -Date Deposited. 2017-02-21T21:27:44ZEPrintshttp://cab.unime.it/images/sitelogo.pnghttp://cab.unime.it/mus/2009-11-26Z2010-04-13T11:14:27Zhttp://cab.unime.it/mus/id/eprint/555This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/5552009-11-26ZQuantum Biology A critical assessment of the recent developments of molecular biology is presented. The thesis that they do not lead to a conceptual understanding of life and biological systems is defended. Maturana and Varela's concept of autopoiesis is briefly sketched and its logical circularity avoided by postulating the existence of underlying living processes, entailing amplification from the microscopic to the macroscopic scale, with increasing complexity in the passage from one scale to the other. Following such a line of thought, the currently accepted model of condensed matter, which is based on electrostatics and short-ranged forces, is criticized. It is suggested that the correct interpretation of quantum dispersion forces (van der Waals, hydrogen bonding, and so on) as quantum coherence effects hints at the necessity of including long-ranged forces (or mechanisms for them) in condensed matter theories of biological processes. Some quantum effects in biology are reviewed and quantum mechanics is acknowledged as conceptually important to biology since without it most (if not all) of the biological structures and signalling processes would not even exist. Moreover, it is suggested that long-range quantum coherent dynamics, including electron polarization, may be invoked to explain signal amplification process in biological systems in general.Alessandro Sergi2009-11-25Z2010-04-13T11:14:58Zhttp://cab.unime.it/mus/id/eprint/533This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/5332009-11-25ZIl metodo della fisica e le problematiche della biologia Following the ancient Hermetic aphorism solve et coagula, we investigate the nature of the interface between physics and biology by moving up and down the different temporal and spatial scales which enter the description of natural phenomena. Various indications seem to support both the existence of such an interface and the possibility of finding methods, languages, and targets shared by such two disciplines. However, this possibility becomes remote if one moves further and further from the microscopic level of atoms and molecules (and, correspondingly, of molecular biology). We conclude that the biologically founded epistemology proposed by Maturana and Varela as well as cultural anthropology and sociology cannot yet be treated with the methodology of physics.
Alessandro SergiGiacomo Tripodi2007-02-13Z2010-04-13T11:17:52Zhttp://cab.unime.it/mus/id/eprint/399This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3992007-02-13ZQuantum-Classical Dynamics of Wave FieldsAn approach to the quantum-classical mechanics of
phase space dependent operators, which has been proposed recently, is remodeled as a formalism for wave fields.
Such wave fields obey a system of coupled non-linear equations that can be written by means of a suitable non-Hamiltonian bracket.
As an example, the theory is applied to the relaxation dynamics of the spin-boson model.
In the adiabatic limit, a good agreement with calculations
performed by the operator approach is obtained.
Moreover, the theory proposed in this paper
can take nonadiabatic effects into account
without resorting to surface-hopping approximations.
Hence, the results obtained follow qualitatively those
of previous surface-hopping calculations
and increase by a factor of (at least) two the time length
over which nonadiabatic dynamics can be propagated
with small statistical errors.
Moreover, it is worth to note that the dynamics of
quantum-classical wave fields here proposed is a straightforward non-Hamiltonian generalization of the formalism for non-linear quantum mechanics that Weinberg introduced recently.Alessandro Sergiasergi@unime.it2006-05-12Z2010-04-13T11:17:55Zhttp://cab.unime.it/mus/id/eprint/392This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3922006-05-12ZQuantum-Classical Dynamics of Wave FieldsThe recent approach to the quantum-classical mechanics of
phase space dependent operators is recast
into a formalism for wave fields.
It turns out that such wave fields
obey a system of coupled non-linear equations where
each equation is not Hermitian. However,
backward and forward time-evolution
is combined in such a way as to conserve probability.
Notwithstanding their non-linear form, the equations of motion
for such phase space dependent wave fields can be
expressed by means of a suitable non-Hamiltonian bracket.
Thus, it can be realized that the non-Hamiltonian dynamics of
quantum-classical wave fields is a straightforward
generalization of the formalism for non-linear
quantum mechanics that Weinberg proposed recently.Alessandro Sergiasergi@unime.it2005-12-02Z2010-04-13T11:19:28Zhttp://cab.unime.it/mus/id/eprint/354This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3542005-12-02ZNon-Hamiltonian Quantum Mechanics.
Relation between operator and wave schemes of motionThe symplectic structure of Weinberg's formalism for nonlinear
quantum mechanics is first unveiled and then generalized
to introduce non-Hamiltonian quantum mechanics.
By exploiting the correspondence between wave
and matrix mechanics, a link between this generalization
and a non-Hamiltonian commutator, proposed recently by this author,
is found.
The general correspondence between operator and wave formalisms
in non-Hamiltonian quantum mechanics
is exploited to introduce a quantum-classical theory
of wave fields.
This can be considered as a first step toward a deeper
understanding of the relation between operator quantum-classical
mechanics, introduced some time ago, and the original
quantum-classical scheme of motion where
wave functions are evolved in time and
the classical degrees of freedom follows
surface-hopping trajectories on single quantum states.Alessandro Sergiasergi@unime.it2005-11-23Z2010-04-13T11:19:36Zhttp://cab.unime.it/mus/id/eprint/350This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3502005-11-23ZOn the Geometry of Non-Hamiltonian Phase SpaceIn this paper the statistical mechanics of canonical,
non-canonical and non-Hamiltonian systems is analyzed rigorously
by throwing light onto the peculiar geometric structure of phase
space. Misleading points, regarding generalized brackets and
Jacobi relations, are clarified. The accessory role of phase space
compressibility in the statistical mechanics of non-canonical and
non-Hamiltonian systems is also unveiled. A rigorous definition of
the (relative) entropy for continuous probability distributions is
adopted and used in order to introduce maximum entropy principles
for non-canonical and non-Hamiltonian systems. Although the
attention is concentrated on the geometry of phase space under
equilibrium thermodynamic conditions, the results and the points of view
presented lay the foundations for a maximum entropy approach to
non-Hamiltonian dissipative systems.Alessandro Sergiasergi@unime.it2005-11-23Z2010-04-13T11:19:39Zhttp://cab.unime.it/mus/id/eprint/351This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3512005-11-23ZStatistical Mechanics of Quantum-Classical Systems with Holonomic ConstraintsThe statistical mechanics of quantum-classical systems
with holonomic constraints
is formulated rigorously by unifying the classical Dirac bracket and the
quantum-classical bracket in matrix form.
The resulting Dirac quantum-classical
theory, which conserves the holonomic constraints exactly, is then used
to formulate time evolution and statistical mechanics.
The correct momentum-jump approximation for constrained system arises
naturally from this formalism.
Finally, in analogy with what was found in the classical case, it
is shown that the rigorous linear
response function of constrained quantum-classical systems
contains non-trivial additional terms which are absent
in the response of unconstrained systems.Alessandro Sergiasergi@unime.it2005-11-14Z2010-04-13T11:19:48Zhttp://cab.unime.it/mus/id/eprint/348This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3482005-11-14ZNon-Hamiltonian Commutators in Quantum MechanicsThe symplectic structure of quantum commutators is first unveiled and then exploited
to introduce generalized non-Hamiltonian brackets in quantum mechanics.
It is easily recognized that quantum-classical systems
are described by a particular realization of such a bracket.
In light of previous work, this introduces
a unified approach to classical and
quantum-classical non-Hamiltonian dynamics.
In order to illustrate the use
of non-Hamiltonian commutators, it is shown how to define
thermodynamic constraints in quantum-classical systems.
In particular, quantum-classical Nos\'e-Hoover equations of motion
and the associated stationary density matrix are derived.
The non-Hamiltonian commutators for both Nos\'e-Hoover chains
and Nos\'e-Andersen (constant-pressure constant temperature)
dynamics are also given.
Perspectives of the formalism are discussed.Alessandro Sergiasergi@unime.it2005-09-26Z2010-04-13T11:20:13Zhttp://cab.unime.it/mus/id/eprint/334This item is in the repository with the URL: http://cab.unime.it/mus/id/eprint/3342005-09-26ZPhase space flows for non-Hamiltonian systems with constraintsIn this paper, non-Hamiltonian systems with holonomic constraints
are treated by a generalization of Dirac's formalism.
Non-Hamiltonian phase space flows can be described
by generalized antisymmetric brackets
or by general Liouville operators which cannot be derived
from brackets. Both situations are treated.
In the first case, a Nos\'e-Dirac
bracket is introduced as an example.
In the second one, Dirac's recipe for
projecting out constrained variables from time translation operators
is generalized and then applied to non-Hamiltonian linear response.
Dirac's formalism avoids spurious terms in the response function
of constrained systems. However, corrections coming from phase
space measure must be considered for general perturbations.Alessandro Sergi