Fermi level alignment in single molecule junctions and its dependence on interface structure

The alignment of the Fermi level of a metal electrode within the gap of the highest occupied and lowest unoccupied orbital of a molecule is a key quantity in molecular electronics. Depending on the type of molecule and the interface structure of the junction, it can vary the electron transparency of a gold/molecule/gold junction by at least one order of magnitude. In this article we will discuss how Fermi level alignment is related to surface structure and bonding configuration on the basis of density functional theory calculations for bipyridine and biphenyl dithiolate between gold leads. We will also relate our findings to quantum-chemical concepts such as electronegativity.Comment: 5 pages, 2 figures, presented at the ICN+T 2006 conferenc

Surface pressure measurements at two tips of a model helicopter rotor in hover

Surface pressures were measured near the tip of a hovering single-bladed model helicopter rotor with two tip shapes. The rotor had a constant-chord, untwisted blade with a square, flat tip which could be modified to a body-of-revolution tip. Pressure measurements were made on the blade surface along the chordwise direction at six radial stations outboard of the 94 percent blade radius. Data for each blade tip configuration were taken at blade collective pitch angles of 0, 6.18 and 11.4 degrees at a Reynolds number of 736,000 and a Mach number of 0.25 both based on tip speed. Chordwise pressure distributions and constant surface pressure contours are presented and discussed

How was the Hubble sequence 6 Gyrs ago?

The way galaxies assemble their mass to form the well-defined Hubble sequence is amongst the most debated topic in modern cosmology. One difficulty is to link distant galaxies to those at present epoch. We aim at establishing how were the galaxies of the Hubble sequence, 6 Gyrs ago. We intend to derive a past Hubble sequence that can be causally linked to the present-day one. We selected samples of nearby galaxies from the SDSS and of distant galaxies from the GOODS survey. We verified that each sample is representative of galaxies. We further showed that the observational conditions necessary to retrieve their morphological classification are similar in an unbiased way. Morphological analysis has been done in an identical way for all galaxies in the two samples. We found an absence of number evolution for elliptical and lenticular galaxies, which strikingly contrasts with the strong evolution of spiral and peculiar galaxies. Spiral galaxies were 2.3 times less abundant in the past, that is exactly compensated by the strong decrease by a factor 5 of peculiar galaxies. It strongly suggests that more than half of the present-day spirals had peculiar morphologies, 6 Gyrs ago, and this has to be accounted by any scenario of galactic disk evolution and formation. The past Hubble sequence can be used to test these scenarios as well as to test evolution of fundamental planes for spirals and bulges.Comment: Version accepted by Astronomy and Astrophysics, October 21 2009. Including low resolution images. 11 pages, 8 figure

Potential Energy Surface for H_2 Dissociation over Pd(100)

The potential energy surface (PES) of dissociative adsorption of H_2 on Pd(100) is investigated using density functional theory and the full-potential linear augmented plane wave (FP-LAPW) method. Several dissociation pathways are identified which have a vanishing energy barrier. A pronounced dependence of the potential energy on ``cartwheel'' rotations of the molecular axis is found. The calculated PES shows no indication of the presence of a precursor state in front of the surface. Both results indicate that steering effects determine the observed decrease of the sticking coefficient at low energies of the H_2 molecules. We show that the topology of the PES is related to the dependence of the covalent H(s)-Pd(d) interactions on the orientation of the H_2 molecule.Comment: RevTeX, 8 pages, 5 figures in uufiles forma

Studies on the numbers of bacteria in milk showing various changes

The relationship between bacteria and the changes that occur in milk has been recognized since the middle of the last century. Certain of the milk abnormalities are almost characteristic of micro-organisms while others, such as abnormal flavors and odors, quite commonly result from causes other than bacterial. Recently the dairy section of the Iowa Agricultural Experiment Station in working with samples of milk from various parts of the state found that milk sometimes received low flavor scores when the number of contained bacteria was exceedingly small, while samples with high flavor scores sometimes contained large numbers of bacteria. This suggested an investigation of the number of organisms required to produce changes in the flavor and odor of milk. The investigation of the odors and flavors produced in milk by bacteria, however, presents certain difficulties. The ordinary sterilization of milk so influences the flavor and odor that those which may be subsequently developed are largely overshadowed. Samples of aseptic milk sometimes have an undesirable flavor and odor that tends to mask other flavors that may be developed. Moreover, the accurate detection of changes in odor and taste presents difficulties because of the varying acuteness of the senses involved. Because of these difficulties much of the work herein reported deals with changes other than those in flavor and odor, such as the production of ropiness, the coagulation of milk and the reduction of litmus milk

A bacteriological study of the method of pasteurizing and homogenizing the ice cream mix.

In continuing the work being carried out at the Iowa Agricultural Experiment Station on the bacteriology of ice cream, 1, 2, a study has been made of the method of pasteurizing and homogenizing the ice cream mix. This method is at present of some commercial importance and apparently its use is increasing. It enables the factory operators to prepare the mixes at their convenience instead of shortly before freezing and thus seems to offer certain advantages insofar as the operation of the plant is concerned. I t was the object of the work herein reported to study the method from the standpoint of its value in the production of ice cream of a high sanitary quality

Slimy and ropy milk

A study of slimy and ropy milk sent for examination to the dairy bacteriological laboratories of Iowa State College has shown the following: 1. Cultures of organisms secured from slimy starters, apparently typical Streptococcus lacticus forms, sometimes showed marked capacity to produce ropiness when inoculated into sterile milk. This slime producing power is evidently a variable characteristic, appearing and disappearing without apparent cause. 2. Associative action of organisms in some cases is responsible for ropiness. Two organisms, neither of which alone can cause ropiness, may, when grown together, cause the medium to become slimy. 3. Bacterium (lactis) viscosum is one common cause of slimy milk. 4. Certain peptonizing bacteria, as Bact. peptogenes, produce a very slimy residuum after digestion of the casein. 5. Bacterium bulgaricum and certain related high acid organisms frequently produce marked viscosity in milk. Sliminess in milk is apparently due to different causes with different organisms: 1. Gum and gum-like capsular materials partially soluble, or at least swelling in water, al\u27e frequently the same. 2. In many cases there seems to be a direct relationship between chain formation of streptococcus and the development of ropiness, likewise between the numbers of bacteria and ropiness. 3. Associative action between two distinct organisms resulting in great increases in number of each is not uncommon as a cause of ropiness. Methods of control and prevention of slimy milk are discussed. Keys to the organisms that have been described as responsible for slimy production in milk are presented. An attempt has been made to clear up synonymy. Descriptions of thirty-three species of bacteria that have been found associated with milk are given, and the literature reviewed

Studies on the development of butter cultures from mixtures of organisms

Studies on the bacteriology of butter cultures have shown that two types of bacteria are normally present, one which attacks primarily the lactose with the formation of large amounts of lactic acid, while the other is characterized by its production of volatile acid from citric acid. These findings suggest the development of butter cultures under carefully controlled conditions by making mixtures of the two types of organisms. While many satisfactory butter cultures have been secured with this procedure, mixtures made with organisms that appear typical on the basis of morphology, cultural characteristics and the usual biochemical tests, often fail to develop a satisfactory aroma and flavor and, accordingly, the percentage of the attempts that are successful is small