American Association for the Advancement of Science (AAAS)
0036-8075
1095-9203
Cơ quản chủ quản: AMER ASSOC ADVANCEMENT SCIENCE , American Association for the Advancement of Science
Lĩnh vực:
History and Philosophy of ScienceMultidisciplinary
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Thông tin về tạp chí
Các bài báo tiêu biểu
Nanophase-Separated Polymer Films as High-Performance Antireflection Coatings Optical surfaces coated with a thin layer to improve light transmission are ubiquitous in everyday optical applications as well as in industrial and scientific instruments. Discovered first in 1817 by Fraunhofer, the coating of lenses became standard practice in the 1930s. In spite of intensive research, broad-band antireflection coatings are still limited by the lack of materials with low refractive indices. A method based on the phase separation of a macromolecular liquid to generate nanoporous polymer films is demonstrated that creates surfaces with high optical transmission.
Tập 283 Số 5401 - Trang 520-522 - 1999
Serial Position Curve in Rats: Role of the Dorsal Hippocampus In an eight-arm radial maze, normal rats demonstrated good immediate retention for the order of first items (primacy component of serial position curve) and last items (recency component of serial position curve) of an eight-item (arm) list. In contrast, rats with dorsal hippocampal lesions displayed, on an immediate retention test, disruption of the primacy but not the recency component of the serial position curve. Furthermore, imposing a 10-minute delay before the retention test impaired all components of the serial position curve. These results support correspondence in mnemonic function of the hippocampus in animals and humans.
Tập 218 Số 4568 - Trang 173-175 - 1982
Long-Term Lymphohematopoietic Reconstitution by a Single CD34-Low/Negative Hematopoietic Stem Cell
Hematopoietic stem cells (HSCs) supply all blood cells throughout life by making use of their self-renewal and multilineage differentiation capabilities. A monoclonal antibody raised to the mouse homolog of CD34 (mCD34) was used to purify mouse HSCs to near homogeneity. Unlike in humans, primitive adult mouse bone marrow HSCs were detected in the mCD34 low to negative fraction. Injection of a single mCD34
lo/−
, c-Kit
+
, Sca-1
+
, lineage markers negative (Lin
−
) cell resulted in long-term reconstitution of the lymphohematopoietic system in 21 percent of recipients. Thus, the purified HSC population should enable analysis of the self-renewal and multilineage differentiation of individual HSCs.
Tập 273 Số 5272 - Trang 242-245 - 1996
Peptide Binding and Release by Proteins Implicated as Catalysts of Protein Assembly Two members of the hsp70 family, termed hsc70 and BiP, have been implicated in promoting protein folding and assembly processes in the cytoplasm and the lumen of the endoplasmic reticulum, respectively. Short hydrophilic (8 to 25 residues) synthetic peptides have now been tested as possible mimics of polypeptide chain substrates to help define an enzymatic basis for these activities. Both BiP and hsc70 have specific peptide binding sites. Peptide binding elicits hydrolysis of adenosine triphosphate, with the subsequent release of bound peptide.
Tập 245 Số 4916 - Trang 385-390 - 1989
Oligonucleotide-Modified Gold Nanoparticles for Intracellular Gene Regulation We describe the use of gold nanoparticle-oligonucleotide complexes as intracellular gene regulation agents for the control of protein expression in cells. These oligonucleotide-modified nanoparticles have affinity constants for complementary nucleic acids that are higher than their unmodified oligonucleotide counterparts, are less susceptible to degradation by nuclease activity, exhibit greater than 99% cellular uptake, can introduce oligonucleotides at a higher effective concentration than conventional transfection agents, and are nontoxic to the cells under the conditions studied. By chemically tailoring the density of DNA bound to the surface of gold nanoparticles, we demonstrated a tunable gene knockdown.
Tập 312 Số 5776 - Trang 1027-1030 - 2006
Identification of Active Gold Nanoclusters on Iron Oxide Supports for CO Oxidation Gold nanocrystals absorbed on metal oxides have exceptional properties in oxidation catalysis, including the oxidation of carbon monoxide at ambient temperatures, but the identification of the active catalytic gold species among the many present on real catalysts is challenging. We have used aberration-corrected scanning transmission electron microscopy to analyze several iron oxide–supported catalyst samples, ranging from those with little or no activity to others with high activities. High catalytic activity for carbon monoxide oxidation is correlated with the presence of bilayer clusters that are ∼0.5 nanometer in diameter and contain only ∼10 gold atoms. The activity of these bilayer clusters is consistent with that demonstrated previously with the use of model catalyst systems.
Tập 321 Số 5894 - Trang 1331-1335 - 2008
Wave-Induced Sediment Transport and Sandbar Migration Onshore sediment transport and sandbar migration are important to the morphological evolution of beaches but are not well understood. Here, a model that accounts for fluid accelerations in waves predicts the onshore sandbar migration observed on an ocean beach. In both the observations and the model, the location of the maximum acceleration-induced transport moves shoreward with the sandbar, resulting in feedback between waves and morphology that drives the bar shoreward until conditions change. A model that combines the effects of transport by waves and mean currents simulated both onshore and offshore bar migration observed over a 45-day period.
Tập 299 Số 5614 - Trang 1885-1887 - 2003
Moving in the Anthropocene: Global reductions in terrestrial mammalian movements Restrictions on roaming
Until the past century or so, the movement of wild animals was relatively unrestricted, and their travels contributed substantially to ecological processes. As humans have increasingly altered natural habitats, natural animal movements have been restricted. Tucker
et al.
examined GPS locations for more than 50 species. In general, animal movements were shorter in areas with high human impact, likely owing to changed behaviors and physical limitations. Besides affecting the species themselves, such changes could have wider effects by limiting the movement of nutrients and altering ecological interactions.
Science
, this issue p.
466
Tập 359 Số 6374 - Trang 466-469 - 2018
Benzodiazepine Peptidomimetics: Potent Inhibitors of Ras Farnesylation In Animal Cells
Oncogenic Ras proteins transform animal cells to a malignant phenotype only when modified by farnesyl residues attached to cysteines near their carboxyl termini. The farnesyltransferase that catalyzes this reaction recognizes tetrapeptides of the sequence
CAAX
, where C is cysteine,
A
is an aliphatic amino acid, and
X
is a carboxyl-terminal methionine or serine. Replacement of the two aliphatic residues with a benzodiazepine-based mimic of a peptide turn generated potent inhibitors of farnesyltransferase [50 percent inhibitory concentration (IC
50
) < 1 nM]. Unlike tetrapeptides, the benzodiazepine peptidomimetics enter cells and block attachment of farnesyl to Ras, nuclear lamins, and several other proteins. At micromolar concentrations, these inhibitors restored a normal growth pattern to Ras-transformed cells. The benzodiazepine peptidomimetics may be useful in the design of treatments for tumors in which oncogenic Ras proteins contribute to abnormal growth, such as that of the colon, lung, and pancreas.
Tập 260 Số 5116 - Trang 1937-1942 - 1993
Human-Induced Changes in the Hydrology of the Western United States Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climate change detection and attribution study, using a high-resolution hydrologic model forced by global climate models, focusing on the changes that have already affected this primarily arid region with a large and growing population. The results show that up to 60% of the climate-related trends of river flow, winter air temperature, and snow pack between 1950 and 1999 are human-induced. These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.
Tập 319 Số 5866 - Trang 1080-1083 - 2008