792 research outputs found
Fragmentation phase transition in atomic clusters I --- Microcanonical thermodynamics
Here we first develop the thermodynamics of microcanonical phase transitions
of first and second order in systems which are thermodynamically stable in the
sense of van Hove. We show how both kinds of phase transitions can
unambiguously be identified in relatively small isolated systems of
atoms by the shape of the microcanonical caloric equation of state
I.e. within microcanonical thermodynamics one does not need to go to the
thermodynamic limit in order to identify phase transitions. In contrast to
ordinary (canonical) thermodynamics of the bulk microcanonical thermodynamics
(MT) gives an insight into the coexistence region. The essential three
parameters which identify the transition to be of first order, the transition
temperature , the latent heat , and the interphase surface
entropy can very well be determined in relatively small
systems like clusters by MT. The phase transition towards fragmentation is
introduced. The general features of MT as applied to the fragmentation of
atomic clusters are discussed. The similarities and differences to the boiling
of macrosystems are pointed out.Comment: Same as before, abstract shortened my e-mail address: [email protected]
Experimental and Theoretical Search for a Phase Transition in Nuclear Fragmentation
Phase transitions of small isolated systems are signaled by the shape of the
caloric equation of state e^*(T), the relationship between the excitation
energy per nucleon e^* and temperature. In this work we compare the
experimentally deduced e^*(T) to the theoretical predictions. The
experimentally accessible temperature was extracted from evaporation spectra
from incomplete fusion reactions leading to residue nuclei. The experimental
e^*(T) dependence exhibits the characteristic S-shape at e^* = 2-3 MeV/A. Such
behavior is expected for a finite system at a phase transition. The observed
dependence agrees with predictions of the MMMC-model, which simulates the total
accessible phase-space of fragmentation
Case records of the Massachusetts General Hospital. Case 3-2006. A 63-year-old woman with jaundice and a pancreatic mass.
Fragmentation Phase Transition in Atomic Clusters II - Coulomb Explosion of Metal Clusters -
We discuss the role and the treatment of polarization effects in many-body
systems of charged conducting clusters and apply this to the statistical
fragmentation of Na-clusters. We see a first order microcanonical phase
transition in the fragmentation of for Z=0 to 8. We can
distinguish two fragmentation phases, namely evaporation of large particles
from a large residue and a complete decay into small fragments only. Charging
the cluster shifts the transition to lower excitation energies and forces the
transition to disappear for charges higher than Z=8. At very high charges the
fragmentation phase transition no longer occurs because the cluster
Coulomb-explodes into small fragments even at excitation energy .Comment: 19 text pages +18 *.eps figures, my e-mail adress: [email protected]
submitted to Z. Phys.
The Multifragmentation Freeze--Out Volume in Heavy Ion Collisions
The reduced velocity correlation function for fragments from the reaction Fe
+ Au at 100 A~MeV bombarding energy is investigated using the
dynamical--statistical approach QMD+SMM and compared to experimental data to
extract the Freeze--Out volume assuming simultaneous multifragmentation.Comment: 8 pages; 3 uuencoded figures available with figures command, LateX,
UCRL-J-1157
The HMGB1/RAGE inflammatory pathway promotes pancreatic tumor growth by regulating mitochondrial bioenergetics
Tumor cells require increased adenosine triphosphate (ATP) to support anabolism and proliferation. The precise mechanisms regulating this process in tumor cells are unknown. Here, we show that the receptor for advanced glycation endproducts (RAGE) and one of its primary ligands, high-mobility group box 1 (HMGB1), are required for optimal mitochondrial function within tumors. We found that RAGE is present in the mitochondria of cultured tumor cells as well as primary tumors. RAGE and HMGB1 coordinately enhanced tumor cell mitochondrial complex I activity, ATP production, tumor cell proliferation and migration. Lack of RAGE or inhibition of HMGB1 release diminished ATP production and slowed tumor growth in vitro and in vivo. These findings link, for the first time, the HMGB1-RAGE pathway with changes in bioenergetics. Moreover, our observations provide a novel mechanism within the tumor microenvironment by which necrosis and inflammation promote tumor progression
A large geometric distortion in the first photointermediate of rhodopsin, determined by double-quantum solid-state NMR
Double-quantum magic-angle-spinning NMR experiments were performed on 11,12-C-13(2)-retinylidene-rhodopsin under illumination at low temperature, in order to characterize torsional angle changes at the C11-C12 photoisomerization site. The sample was illuminated in the NMR rotor at low temperature (similar to 120 K) in order to trap the primary photointermediate, bathorhodopsin. The NMR data are consistent with a strong torsional twist of the HCCH moiety at the isomerization site. Although the HCCH torsional twist was determined to be at least 40A degrees, it was not possible to quantify it more closely. The presence of a strong twist is in agreement with previous Raman observations. The energetic implications of this geometric distortion are discussed
Toward An Understanding Of The Retinal Chromophore In Rhodopsin Mimics
Recently, a rhodopsin protein mimic was constructed by combining mutants of the cellular retinoic acid binding protein II (CRABPII) with an all-trans retinal chromophore. Here, we present a combine computational quantum mechanics/molecular mechanics (QM/MM) and experimental ultrafast kinetic study of CRABPII. We employ the QM/MM models to study the absorption (lambda(a)(max)), fluorescence (lambda(f)(max)), and reactivity of a CRABPII triple mutant incorporating the all-trans protonated chromophore (PSB-KLE-CRABPII). We also study the spectroscopy of the same mutant incorporating the unprotonated chromophore and of another double mutant incorporating the neutral unbound retinal molecule held inside the pocket. Finally, for PSB-KLE-CRABPII, stationary fluorescence spectroscopy and ultrafast transient absorption spectroscopy resolved two different evolving excited state populations which were computationally assigned to distinct locally excited and charge-transfer species. This last species is shown to evolve along reaction paths describing a facile isomerization of the biologically relevant 11-cis and 13-cis double bonds. This work represents a first exploratory attempt to model and study these artificial protein systems. It also indicates directions for improving the QM/MM models so that they could be more effectively used to assist the bottom-up design of genetically encodable probes and actuators employing the retinal chromophore
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