Liquid-liquid phase coexistence in gold clusters: 2D or not 2D?

The thermodynamics of gold cluster anions (AuN-, N=11,...,14) is investigated using quantum molecular dynamics. Our simulations suggest that AuN- may exhibit a novel, freestanding planar liquid phase which dynamically coexists with a normal three-dimensional liquid. Upon cooling with experimentally realizable cooling rates, the entropy-favored three-dimensional liquid clusters often supercool and solidify into the "wrong" dimensionality. This indicates that experimental validation of theoretically predicted AuN- ground states might be more complicated than hitherto expected.     

Radiation-induced kidney injury: a role for chronic oxidative stress?

Kidney irradiation clearly leads to a progressive reduction in function associated with concomitant glomerulosclerosis and/or tubulointerstitial fibrosis. However, the particular cell types, mediators and/or mechanisms involved in the development and progression of radiation nephropathy remain ill defined. Angiotensin II (Ang II) plays a major pathogenic role; administration of Ang II blockers markedly abrogates the severity of radiation nephropathy in experimental models. Both ionizing radiation and Ang II signal via generation of reactive oxygen species (ROS). Thus, we hypothesized that localized kidney irradiation might lead to a chronic oxidative stress. In view of the difficulty in measuring ROS in vivo we adopted an indirect immunohistochemical approach in which we used a monoclonal antibody specific for 8-hydroxy-2'-deoxyguanosine (8-OHdG), one of the most commonly used markers of DNA oxidation.The right kidney of 7-8 week-old male Sprague-Dawley rats was removed. Five to 6 weeks later the remaining hypertrophied kidney was irradiated with single doses of 0-20.0 Gy X-rays. Groups of rats, three per dose, were killed at 4, 8, 16 and 24 weeks post-irradiation, their kidneys fixed, and sections stained with the 8-OHdG-specific antibody N45.1.For quantitation of glomerular DNA oxidation with the N45.1 antibody stained sections, 50 glomeruli/animal were counted. The presence of any intensely stained nuclei within the glomerular tuft was scored as positive. Quantitation of tubular DNA oxidation employed a 10 x 10 point ocular grid. Sections were examined at 400 magnification; 250 tubular profiles were counted. All tubules with any nuclear staining were scored as positive.Sham-irradiated kidneys showed little evidence of DNA oxidation over the experimental period. In contrast, localized kidney irradiation led to a marked, dose-independent increase in glomerular and tubular cell nuclear DNA oxidation. This increase was evident at the first time point studied, i.e. 4 weeks after irradiation, and persisted for up to 24 weeks postirradiation. DNA oxidation in the irradiated kidney was only seen in apparently viable glomerular and tubular cells. Thus, while from 16 to 24 weeks post-irradiation structural alterations had progressed to glomerular sclerosis and tubular atrophy, positive staining for 8-OHdG was not observed in severely atrophic tubules. Similarly, fewer positive staining cells were noted in glomeruli undergoing sclerosis, while none were seen in totally sclerotic glomeruli. These data support the hypothesis that renal irradiation is associated with a chronic and persistent oxidative stress.     

New force or model-dependent effect in the mine gravity measurements?

The exact solution for the oblate spheroidal layer model of the earth is applied to recent gravity data measured at the Hilton mine, Mount Isa, Queensland. We find that our extracted values of the gravitational constant from the Hilton mine data are consistent with the laboratory value within the accuracy of the mass density profile determination made at the Hilton mine and the surrounding area.     

Towards a Resolution of Dilemma: Nonlocality or Nonobjectivity?

This paper discusses a possible resolution of the nonobjectivity-nonlocality dilemma in quantum mechanics in the light of experimental tests of the Bell inequality for two entangled photons and a Bell-like inequality for a single neutron. My conclusion is that these experiments show that quantum mechanics is nonobjective: that is, the values of physical observables cannot be assigned to a system before measurement. Bell’s assumption of nonlocality has to be rejected as having no direct experimental confirmation, at least thus far. I also consider the relationships between nonobjectivity and contextuality. Specifically, I analyze the impact of the Kochen-Specker theorem on the problem of contextuality of quantum observables. I argue that, just as von Neumann’s “no-go” theorem, the Kochen-Specker theorem is based on assumptions that do not correspond to the real physical situation. Finally, I present a theory of measurement based on a classical, purely wave model (pre-quantum classical statistical field theory), a model that reproduces quantum probabilities. In this model continuous fields are transformed into discrete clicks of detectors. While this model is classical, it is nonobjective. In this case, nonobjectivity is the result of the dependence of experimental outcomes on the context of measurement, in accordance with Bohr’s view.     

Does gold cluster promote or scavenge radicals? A controversy at DFT

Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au₃ cluster on RO^? vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n‐propyl, i‐propyl, n‐butyl, t‐butyl, and phenyl). In the presence of Au₃ cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO^? oxygen are reduced dramatically. These are clear evidences for both the Au₃ facilitation of the RO–H bond breakage and its scavenging of RO^? radical. Since O–Au anchoring bond is responsible for the interaction of Au₃ cluster and ROH (or RO^?), its nature was interpreted by means of the quantum theory of atoms in molecules and the natural bond orbital. The results indicate that O–Au bond is stronger and has more covalent character in RO^?–Au₃ than in ROH–Au₃. The interaction of Au₃ cluster with RO^? is 1.5 to 3 times more than that with ROH. As a result, gold cluster scavenging property appears more prominent than its free radical initiation activity.     

Structure of a collapsed polymer chain with stickers: a single- or multiflower?

Using an amphiphilic copolymer with evenly spaced hydrophobic styrene segments (stickers), poly(N-isopropylacrylamide-s-styrene), we recently confirmed a long-standing prediction that such a copolymer chain in a solvent selectively poor for the stickers could self-fold from a random coil to a single-flowerlike core-shell nanostructure. Moreover, we found that the self-folding involves the movement of the sticks to the center and the transition from the random coil to the collapsed globule passes through a proposed ordered coil state.     

Collisions between a single gold atom and 13 atom gold clusters: an ab initio approach

Collision processes between a single gold atom and a gold cluster are investigated by means of ab initio techniques. The targets we consider are minimum energy 13 gold atom clusters. The kinetic energy of the projectile and its impact parameter are chosen within a range such that the three regimes we are mainly interested in studying (fusion, scattering and fragmentation) are realized. The results of the collision processes are treated using density functional theory molecular dynamics (DFT-MD), analyzed in detail, and compared with previous work, which was carried out using phenomenological potentials and classical molecular dynamics. The differences between classical MD and DFT-MD are quite significant.     

Charm in PHENIX—a signal or a background?

Charm, as well as Strangeness, plays an important role in searches for the Quark Gluon Plasma.J/Φ Suppression and Strangeness Enhancement are two of the earliest proposed QGP signatures. Recent theoretical work on charm in Relativistic Heavy Ion collisions has focussed on di-lepton production. However, even before the discovery of theJ/Ψ, evidence of open charm was seen in hadron collisions via the observation of promptsingle leptons “resulting from the semi-leptonic decays of charm particles.” [1] The ‘copious’ yield of direct (i.e. not from Dalitz decays) single electrons and muons—at a levele/π～10^?4 forpT≥1.3 GeV/c—observed in the early 1970’s was explained by Hinchliffe and Llewellyn-Smith and Bourquin and Gaillard as evidence of open-charm production. It is likely thate/π at RHIC is large and is a good measure of charm production. Thus, a measurement of single electrons with moderatepT>1.5 GeV/c at RHIC should give a clean charm signal in heavy ion collisions,with no combinatoric background.     

Nanosciences: Evolution or revolution?

In miniaturized objects fabricated by modern technology the smallest linear size may be of a few nanometers. In the field of microelectronics, the advantages of such a miniaturization are huge (increased complexity and reliability, reduced costs). The technology is now approaching the limits where further size reduction will be impossible, except for very novel techniques such as molecular electronics. Miniaturization research has also led to the discovery of nanometric objects such as carbon nanotubes, which turn out to be particularly appropriate for inventing new materials. Miniaturization techniques have been progressively applied in other fields, with the hope of obtaining improvements similar to those encountered in microelectronics. Examples are biochips, which concentrate on a few cm² the recognition of ADN sequences, or ‘lab-on-a-chip’ devices, each of which constitutes a whole laboratory of chemical analysis, or MEMs (Micro Electro Mechanical Systems). New therapies will use miniaturized objects with multiple functions: For instance a nanoparticle can both recognize the target organ thanks to an appropriate protein, and deliver the therapeutic molecule to this target. These results have only been possible through new observation instruments, able to observe and manipulate nano objects. Is the observed evolution really a revolution of science and techniques? This is a point discussed in the conclusion, which also deals with risks associated to nanotechnologies, while the need for a social regulation is stressed.     

“Gold corrosion”: red stains on a gold Austrian Ducat

Femtosecond laser induced adsorption site changes of CO at nanoparticulate palladium aggregates have been investigated using laser light at =400 nm and pulse lengths of 70 fs. The average sizes of the aggregates grown by evaporating palladium atoms onto an epitaxial Al₂O₃ film on NiAl(110) were varied between 100 and 6000 atoms per island. Amorphous aggregates grown at 120 K and crystalline aggregates grown at 300 K have been investigated. Beyond laser-induced migration of CO already reported for nanosecond experiments, adsorbate-induced surface roughening is apparent from Fourier-transform infrared reflection absorption spectroscopy. The laser-induced processes are correlated to the presence of higher local adsorbate densities and a substantial population of edge sites. A model is suggested attributing surface roughening to the formation of local hot spots after coherent electronic excitation via heating through highly vibrationally excited adsorbate states and energetic channelling along chains of elevated local adsorbate densities. The processes are most efficient for intermediate aggregate sizes. In contrast to nanosecond experiments, a few percent of CO molecules are desorbed during the femtosecond experiments from smaller aggregates. PACS 82.53.St     

Number of revolutions of a particle around a black hole: Is it infinite or finite?

We consider a particle falling into a rotating black hole. Such a particle makes an infinite number of revolutions n from the viewpoint of a remote observer who uses the Boyer–Lindquist type of coordinates. We examine the behavior of n when it is measured with respect to a local reference frame that also rotates due to dragging effect of spacetime. The crucial point consists here in the observation that for a nonextremal black hole, the leading contributions to n from a particle itself and the reference frame have the same form being in fact universal, so that divergences mutually cancel. As a result, the relative number of revolutions turns out to be finite. For the extremal black hole this is not so, n can be infinite. Different choices of the local reference frame are considered, the results turn out to be the same qualitatively. For illustration, we discuss two explicit examples—rotation in the flat spacetime and in the Kerr metric.     

The state vector of a quantum system: Mathematical fiction or physical reality?

A version of an experiment with a correlated pair of entangled particles is considered. This experiment demonstrates an interesting effect of variations in the entangled photon polarization that shows the reality of all of the various superposition components and the corresponding state vector of the quantum system. The possible consequences of this are analyzed.     

Causal nets or what is a deterministic computation?

The network approach to computation is more direct and physical than the one based on some specific computing devices (like Turing machines). However, the size of a usual—e.g., Boolean—network does not reflect the complexity of computing the corresponding function, since a small network may be very hard to find even if it exists. A history of the work of a particular computing device can be described as a network satisfying some restrictions. The size of this network reflects the complexity of the problem, but the restrictions are usually somewhat arbitrary and even awkward. Causal nets are restricted only by determinism (causality) and locality of interaction. Their geometrical characteristics do reflect computational complexities. And various imaginary computer devices are easy to express in their terms. The elementarily of this concept may help bringing geometrical and algebraic (and maybe even physical) methods into the theory of computations. This hope is supported by the group-theoretical criterion given in this paper for computability from symmetrical initial configurations.Part of this work was done while this author was visiting Johann Wolfgang Goethe University, Frankfurt am Main in 1978 and Stanford University in 1979.The research of this author was partially supported by NSF grants MCS 77-19754 and MCS-8104211.     

Nucleon Strangeness: Intrinsic or Extrinsic?

A review of experimental results for the measurement of the strange quark distributions in the nucleon, is given. Contributions of the strange quarks to the nucleon mass, electromagnetic form factors and spin, are discussed.     

Forward masking: adaptation or integration?

The aim of this study was to attempt to distinguish between neural adaptation and persistence (or temporal integration) as possible explanations of forward masking. Thresholds were measured for a sinusoidal signal as a function of signal duration for conditions where the delay between the masker offset and the signal offset (the offset-offset interval) was fixed. The masker was a 200-ms broadband noise, presented at a spectrum level of 40 dB (re: 20 microPa), and the signal was a 4-kHz sinusoid, gated with 2-ms ramps. The offset-offset interval was fixed at various durations between 4 and 102 ms and signal thresholds were measured for a range of signal durations at each interval. A substantial decrease in thresholds was observed with increasing duration for signal durations up to about 20 ms. At short offset-offset intervals, the amount of temporal integration exceeded that normally found in quiet. The results were simulated using models of temporal integration (the temporal-window model) and adaptation. For both models, the inclusion of a peripheral nonlinearity, similar to that observed physiologically in studies of the basilar membrane, was essential in producing a good fit to the data. Both models were about equally successful in accounting for the present data. However, the temporal-window model provided a somewhat better account of similar data from a simultaneous-masking experiment, using the same parameters. This suggests that the linear, time-invariant properties of the temporal-window approach are appropriate for modeling forward masking. Overall the results confirm that forward masking can be described in terms of peripheral nonlinearity followed by linear temporal integration at higher levels in the auditory system. However, the difference in predictions between the adaptation and integration models is relatively small, meaning that influence of adaptation cannot be ruled out.     

Vortex collisions: crossing or recombination?

We investigate the collision of two vortex lines moving with viscous dynamics and driven towards each other by an applied current. Using London theory in the approach phase we observe a nontrivial vortex conformation producing antiparallel segments; their attractive interaction triggers a violent collision. The collision region is analyzed using the time-dependent Ginzburg-Landau equation. While we find that vortices will always recombine through the exchange of segments, a crossing channel appears naturally through a double collision process.     

Mössbauer analysis of BIOX treatment of ores at Wiluna gold mine, Western Australia

Mössbauer phase analysis of samples taken from nine stages of the bacterial oxidation processing of gold ore at the Wiluna Gold Mine followed the transformation of the arsenopyrite/pyrite minerals. The principal end-stage phases were szomolnokite, ferric oxyhydroxides, ferric arsenates, jarosite and incompletely transformed pyrite, with higher hydrates of ferrous sulphate being created and then dehydrating to szomolnokite during the processing.