Spontaneous formation of macroscopic chiral domains in a fluid smectic phase of achiral molecules     

DR Link  G Natale  R Shao  JE Maclennan  NA Clark  E Korblova  DM Walba 《Science (New York, N.Y.)》1997,278(5345):1924-1927

A smectic liquid-crystal phase made from achiral molecules with bent cores was found to have fluid layers that exhibit two spontaneous symmetry-breaking instabilities: polar molecular orientational ordering about the layer normal and molecular tilt. These instabilities combine to form a chiral layer structure with a handedness that depends on the sign of the tilt. The bulk states are either antiferroelectric-racemic, with the layer polar direction and handedness alternating in sign from layer to layer, or antiferroelectric-chiral, which is of uniform layer handedness. Both states exhibit an electric field-induced transition from antiferroelectric to ferroelectric.  相似文献   

Organic Glasses: A New Class of Photorefractive Materials     

PM Lundquist  R Wortmann  C Geletneky  RJ Twieg  M Jurich  VY Lee  CR Moylan  DM Burland 《Science (New York, N.Y.)》1996,274(5290):1182-1185

The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties.  相似文献   

Expression in Escherichia coli of open reading frame gene segments of HTLV-III   总被引：6，自引：0，他引：6  

N T Chang  P K Chanda  A D Barone  S McKinney  D P Rhodes  S H Tam  C W Shearman  J Huang  T W Chang  R C Gallo 《Science (New York, N.Y.)》1985,228(4695):93-96

Human T-cell lymphotropic virus type III (HTLV-III), the causative agent of the acquired immune deficiency syndrome (AIDS), was recently isolated and its genomic structure analyzed by DNA cloning methods. In the studies reported here a combined cloning and expression system was used to identify HTLV-III encoded peptides that react immunologically with antibodies in sera from AIDS patients. Cloned HTLV-III DNA was sheared into approximately 500-base-pair fragments and inserted into an "open reading frame" expression vector, pMR100. The inserted DNA was expressed in Escherichia coli transformants as a polypeptide fused to the lambda CI protein at its amino terminus and to beta-galactosidase at its carboxyl terminus. Sera from AIDS patients containing antibodies to HTLV-III were then used to screen for immunoreactive fusion proteins. Twenty clones, each specifying a fusion protein strongly reactive with AIDS serum, were identified. DNA sequence analysis indicated that the HTLV-III fragments were derived from the open reading frame DNA segments corresponding to the gag and pol gene coding regions and also the large open reading frame region (env-lor) located near the 3' end of the viral genome.  相似文献   

Nanofabrication of Small Copper Clusters on Gold(111) Electrodes by a Scanning Tunneling Microscope     

DM Kolb  R Ullmann  T Will 《Science (New York, N.Y.)》1997,275(5303):1097-1099

The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and "conducting wires" in a very flexible and convenient manner.  相似文献   

Detecting explosives     

Devolpi A  Rhodes EA 《Science (New York, N.Y.)》1992,258(5079):14-15

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Radioactive elements on Mercury's surface from MESSENGER: implications for the planet's formation and evolution     

Peplowski PN  Evans LG  Hauck SA  McCoy TJ  Boynton WV  Gillis-Davis JJ  Ebel DS  Goldsten JO  Hamara DK  Lawrence DJ  McNutt RL  Nittler LR  Solomon SC  Rhodes EA  Sprague AL  Starr RD  Stockstill-Cahill KR 《Science (New York, N.Y.)》2011,333(6051):1850-1852

The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury's northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent with physical models for the formation of Mercury requiring extreme heating of the planet or its precursor materials, and supports formation from volatile-containing material comparable to chondritic meteorites. Abundances of K, Th, and U indicate that internal heat production has declined substantially since Mercury's formation, consistent with widespread volcanism shortly after the end of late heavy bombardment 3.8 billion years ago and limited, isolated volcanic activity since.  相似文献   

Synthesis and studies with labeled bromacil 2-C14 and terbacil     

Gardiner JA  Rhodes RC  Adams JB  Soboczenski EJ 《Journal of agricultural and food chemistry》1969,17(5):980-986

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Sulphur gas emissions in the boreal forest: The west whitecourt case study IV: Air quality and the meteorological environment     

P. F. Lester  E. C. Rhodes  A. H. Legge 《Water, air, and soil pollution》1986,27(1-2):85-108

A program of atmospheric measurements was carried out in support of the West Whitecourt case study in the summers of 1975 and 1976. Measurements in and around an isolated stand of mature lodgepole × Jack pine trees included temperature, moisture, and wind measurements at a climatological station outside the stand and at several levels on a 30 m radio mast tower within the stand. Sulphur dioxide concentrations were also measured on the tower. A number of short-term, intensive measurements were made to document the meteorological and SO₂ environments in more detail, with special attention given to the transport of S gas from the source to the sink. The major source of SO₂ at the intensive experimental site was very likely the flare stacks at the gas processing plant. Sulphur dioxide events at the study site were typically daytime, low concentration bursts of a few minutes in duration which occurred with westerly winds under fair weather conditions. Air impinging on the stand tended to flow around the edges of the stand, over the canopy, and into the trunk space. This aerodynamic effect, together with the uptake of SO₂ by the vegetation, caused a minimum in SO₂ concentration in the crown of the forest.  相似文献   

Binding affinity of hydrolyzable tannins to parotid saliva and to proline-rich proteins derived from it     

Bacon JR  Rhodes MJ 《Journal of agricultural and food chemistry》2000,48(3):838-843

Proline-rich proteins (PRP) in human parotid saliva have a high affinity for dietary polyphenolic compounds (tannins), forming stable complexes that may modulate the biological and nutritional properties of the tannin. The formation of such complexes may also have an important role in the modulation or promotion of the sensation of oral astringency perceived when tannin-rich foods and beverages are consumed. The major classes of PRP (acidic, basic, and glycosylated) have been isolated from human saliva, and the relative binding affinities of a series of hydrolyzable tannins, which are found in a number of plant-derived foods and beverages, to these PRP classes have been determined using a competition assay. All of the classes of PRP have a high capacity for hydrolyzable tannins. Within the narrow range of binding affinities exhibited, structure/binding relationships with the levels of tannin galloylation, hexahydroxydiphenoyl esterification, and degree of polymerization were identified. No individual class of human salivary PRP appears to have an exclusive affinity for a particular type of hydrolyzable tannin.  相似文献   

Effects of Fluorides in Animals          下载免费PDF全文

C. S. Rhodes 《The Canadian veterinary journal. La revue veterinaire canadienne》1975,16(5):150

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