441 research outputs found
Variational Methods for Nuclear Systems with Dynamical Mesons
We derive a model Hamiltonian whose ground state expectation value of any
two-body operator coincides with that obtained with the Jastrow correlated wave
function of the many-body Fermi system. Using this Hamiltonian we show that the
variational principle can be extended to treat systems with dynamical mesons,
even if in this case the concept of wave function looses its meaning
Functional approach to the electromagnetic response function: the Longitudinal Channel
In this paper we address the (charge) longitudinal electromagnetic response
for a homogeneous system of nucleons interacting via meson exchanges in the
functional framework. This approach warrants consistency if the calculation is
carried on order-by-order in the mesonic loop expansion with RPA-dressed
mesonic propagators. At the 1-loop order and considering pion, rho and omega
exchanges we obtain a quenching of the response, in line with the experimental
results.Comment: RevTeX, 18 figures available upon request - to be published in
Physical Review
Path Integral Variational Methods for Strongly Correlated Systems
We introduce a new approach to highly correlated systems which generalizes
the Fermi Hypernetted Chain and Correlated Basis Function techniques. While the
latter approaches can only be applied to systems for which a nonrelativistic
wave function can be defined, the new approach is based on the variation of a
trial hamiltonian within a path integral framework and thus can also be applied
to relativistic and field theoretical problems. We derive a diagrammatic scheme
for the new approach and show how a particular choice of the trial hamiltonian
corresponds exactly to the use of a Jastrow correlated ansatz for the wave
function in the Fermi Hypernetted Chain approach. We show how our new approach
can be used to find upper bounds to ground state energies in systems which the
FHNC cannot handle, including those described by an energy-dependent effective
hamiltonian. We demonstrate our approach by applying it to a quantum field
theoretical system of interacting pions and nucleons.Comment: 35 RevTeX pages, 7 separated ps figures available on reques
Spin projected unrestricted Hartree-Fock ground states for harmonic quantum dots
We report results for the ground state energies and wave functions obtained
by projecting spatially unrestricted Hartree Fock states to eigenstates of the
total spin and the angular momentum for harmonic quantum dots with
interacting electrons including a magnetic field states with the correct
spatial and spin symmetries have lower energies than those obtained by the
unrestricted method. The chemical potential as a function of a perpendicular
magnetic field is obtained. Signature of an intrinsic spin blockade effect is
found.Comment: 12 pages, 5 tables, 10 figures, submitted to Phys. Rev.
The multilevel pairing Hamiltonian versus the degenerate case
We study the pairing Hamiltonian in a set of non degenerate levels. First, we
review in the path integral framework the spontaneous breaking of the U(1)
symmetry occurring in such a system for the degenerate situation. Then the
behaviors with the coupling constant of the ground state energy in the
multilevel and in the degenerate case are compared. Next we discuss, in the
multilevel case, an exact strong coupling expansion for the ground state energy
which introduces the moments of the single particle level distribution. The
domain of validity of the expansion, which is known in the macroscopic limit,
is explored for finite systems and its implications for the energy of the
latter is discussed. Finally the seniority and Gaudin excitations of the
pairing Hamiltonian are addressed and shown to display the same gap in leading
order.Comment: 20 pages, 4 figure
System consolidation of spatial memories in mice: effects of enriched environment.
Environmental enrichment (EE) is known to enhance learning and memory. Declarative memories are thought to undergo a first rapid and local consolidation process, followed by a prolonged process of system consolidation, which consist in a time-dependent gradual reorganization of brain regions supporting remote memory storage and crucial for the formation of enduring memories. At present, it is not known whether EE can affect the process of declarative memory system consolidation. We characterized the time course of hippocampal and cortical activation following recall of progressively more remote spatial memories. Wild-type mice either exposed to EE for 40 days or left in standard environment were subjected to spatial learning in the Morris water maze and to the probe test 1, 10, 20, 30, and 50 days after learning. Following the probe test, regional expression of the inducible immediate early gene c-Fos was mapped by immunohistochemistry, as an indicator of neuronal activity. We found that activation of the medial prefrontal cortex (mPFC), suggested to have a privileged role in processing remote spatial memories, was evident at shorter time intervals after learning in EE mice; in addition, EE induced the progressive activation of a distributed cortical network not activated in non-EE mice. This suggests that EE not only accelerates the process of mPFC recruitment but also recruits additional cortical areas into the network supporting remote spatial memories
Inclusive versus Exclusive EM Processes in Relativistic Nuclear Systems
Connections are explored between exclusive and inclusive electron scattering
within the framework of the relativistic plane-wave impulse approximation,
beginning with an analysis of the model-independent kinematical constraints to
be found in the missing energy--missing momentum plane. From the interplay
between these constraints and the spectral function basic features of the
exclusive and inclusive nuclear responses are seen to arise. In particular, the
responses of the relativistic Fermi gas and of a specific hybrid model with
confined nucleons in the initial state are compared in this work. As expected,
the exclusive responses are significantly different in the two models, whereas
the inclusive ones are rather similar. By extending previous work on the
relativistic Fermi gas, a reduced response is introduced for the hybrid model
such that it fulfills the Coulomb and the higher-power energy-weighted sum
rules. While incorporating specific classes of off-shellness for the struck
nucleons, it is found that the reducing factor required is largely
model-independent and, as such, yields a reduced response that is useful for
extracting the Coulomb sum rule from experimental data. Finally, guided by the
difference between the energy-weighted sum rules of the two models, a version
of the relativistic Fermi gas is devised which has the 0, 1 and 2 moments of the charge response which agree rather well
with those of the hybrid model: this version thus incorporates {\em a priori}
the binding and confinement effects of the stuck nucleons while retaining the
simplicity of the original Fermi gas.Comment: LaTex file with 15 .ps figure
Time-lapse monitoring of root water uptake using electrical resistivity tomography and mise-Ă -la-masse: a vineyard infiltration experiment
Abstract. This paper presents a time-lapse application of
electrical methods (electrical resistivity tomography, ERT; and
mise-Ă -la-masse, MALM) for monitoring plant roots and their activity
(root water uptake) during a controlled infiltration experiment. The use of
non-invasive geophysical monitoring is of increasing interest as these
techniques provide time-lapse imaging of processes that otherwise can only
be measured at few specific spatial locations. The experiment here described was conducted in a vineyard in Bordeaux (France) and was focused on the
behaviour of two neighbouring grapevines. The joint application of ERT and
MALM has several advantages. While ERT in time-lapse mode is sensitive to
changes in soil electrical resistivity and thus to the factors controlling
it (mainly soil water content, in this context), MALM uses DC current
injected into a tree stem to image where the plant root system is in effective
electrical contact with the soil at locations that are likely to be the same
where root water uptake (RWU) takes place. Thus, ERT and MALM provide
complementary information about the root structure and activity. The
experiment shows that the region of likely electrical current sources
produced by MALM does not change significantly during the infiltration time
in spite of the strong changes of electrical resistivity caused by changes
in soil water content. Ultimately, the interpretation of the current source
distribution strengthened the hypothesis of using current as a proxy for
root detection. This fact, together with the evidence that current injection
in the soil and in the stem produces totally different voltage patterns,
corroborates the idea that this application of MALM highlights the active
root density in the soil. When considering the electrical resistivity
changes (as measured by ERT) inside the stationary volume of active roots
delineated by MALM, the overall tendency is towards a resistivity increase
during irrigation time, which can be linked to a decrease in soil water
content caused by root water uptake. On the contrary, when considering the
soil volume outside the MALM-derived root water uptake region, the
electrical resistivity tends to decrease as an effect of soil water content
increase caused by the infiltration. The use of a simplified infiltration
model confirms at least qualitatively this behaviour. The monitoring results
are particularly promising, and the method can be applied to a variety of
scales including the laboratory scale where direct evidence of root
structure and root water uptake can help corroborate the approach. Once
fully validated, the joint use of MALM and ERT can be used as a valuable
tool to study the activity of roots under a wide variety of field
conditions
APPROCCIO MULTI-DISCIPLINARE AL PROBLEMA DELLA SUBSIDENZA NELLA REGIONE EMILIA ROMAGNA
L’estrazione di fluidi sotterranei ha prodotto significativi fenomeni di subsidenza nel territorio della
Regione Emilia-Romagna. Al fine di analizzare il fenomeno, per meglio comprenderne l’origine e
gli aspetti evolutivi, è stato utilizzato un approccio multidisciplinare basato su innovativi sistemi di
controllo delle quote piezometriche dei pozzi e degli spostamenti della superficie topografica. In
particolare mediante la tecnica di interferometria DInSAR – SBAS sono state elaborate 52
immagini distribuite su un’area compresa tra l’Appennino bolognese e il fiume Po. E’ stata inoltre
studiata l’evoluzione temporale delle quote piezometriche dei pozzi presenti in Regione, con lo
scopo di evidenziare aree potenzialmente soggette a subsidenza confrontabile con i dati di
spostamento al suolo DInSAR e con dati geodetici (livellazioni e dati GPS). Un significativo
miglioramento della conoscenza dei fenomeni di subsidenza potrĂ avvenire integrando i risultati
ottenuti con i dati forniti dalla nuova rete di stazioni GPS permanenti progettata congiuntamente
dall’INGV e dall’Università di Bologna. L’analisi di dati geologici, idrogeologici, telerilevati e
geodetici ha portato a risultati significativi per una corretta comprensione dei processi di subsidenza
su buona parte della città di Bologna e della sua provincia. Tale approccio verrà esteso a tutta l’area
compresa tra la catena appenninica ed il fiume Po
Autophagic degradation of farnesylated prelamin A as a therapeutic approach to lamin-linked progeria
Farnesylated prelamin A is a processing intermediate produced in the lamin A maturation pathway. Accumulation of a truncated farnesylated prelamin A form, called progerin, is a hallmark of the severe premature ageing syndrome, Hutchinson-Gilford progeria. Progerin elicits toxic effects in cells, leading to chromatin damage and cellular senescence and ultimately causes skin and endothelial defects, bone resorption, lipodystrophy and accelerated ageing. Knowledge of the mechanism underlying prelamin A turnover is critical for the development of clinically effective protein inhibitors that can avoid accumulation to toxic levels without impairing lamin A/C expression, which is essential for normal biological functions. Little is known about specific molecules that may target farnesylated prelamin A to elicit protein degradation. Here, we report the discovery of rapamycin as a novel inhibitor of progerin, which dramatically and selectively decreases protein levels through a mechanism involving autophagic degradation. Rapamycin treatment of progeria cells lowers progerin, as well as wild-type prelamin A levels, and rescues the chromatin phenotype of cultured fibroblasts, including histone methylation status and BAF and LAP2α distribution patterns. Importantly, rapamycin treatment does not affect lamin C protein levels, but increases the relative expression of the prelamin A endoprotease ZMPSTE24. Thus, rapamycin, an antibiotic belonging to the class of macrolides, previously found to increase longevity in mouse models, can serve as a therapeutic tool, to eliminate progerin, avoid farnesylated prelamin A accumulation, and restore chromatin dynamics in progeroid laminopathies
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