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65Cu NMR and 65Cu−27Al spin-echo, double-resonance (SEDOR) measurements from Cu-exchanged ZSM-5 catalysts are reported. The presence of Cu+ cations in CuZSM-5 was detected directly by 65Cu NMR; upon heating, we observed the autoreduction of Cu2+ to Cu+. It was found that the Cu+ cations can be reduced further to Cu0 by exposure to carbon monoxide at high temperatures. The internuclear distance between the two quadrupolar nuclei Cu (spin-3/2) and Al (spin-5/2) was determined to be 0.23 ± 0.02 nm, in good agreement with the value of 0.24 nm obtained from density functional theory calculations.
Social workers are seeing, in health care settings, an increasing number of grandparent caregivers among their clients. A disproportionate number of these are African American. This article compares the demographic and physical and mental health characteristics of African American grandparents who are raising their grandchildren with non-caregiving African American grandparents, using the National Survey of Families and Households (1992-94). Caregivers reported significantly higher levels of limitations in four of five activities of daily living (ADL) and were almost twice as likely as their peers to report clinically relevant levels of depression.
The light-independent recovery of the photosynthetic apparatus from photoinhibition was monitored upon a transition of irradiance-stressed Dunaliella salina Teod. to darkness. Upon dark incubation, the chlorophyll (Chl) a /Chl b ratio of the cells decreased promptly with a half-time of 2.5 h from about 12:1 to about 5:1. In contrast, dark incubation of control cells resulted in only a negligible change of the Chl a /Chl b ratio. During dark incubation of irradiance-stressed cells, the level of the Chl a and b light-harvesting proteins of photosystem II (PSII) increased, a change accompanied by alterations in the composition of these light-harvesting proteins. The amount of photodamaged PSII, measured from the relative amount of a 160 kDa protein complex which contains the photodamaged D1 reaction center protein, decreased during dark incubation after an initial lag period. Concomitantly, the amount of functional PSII, measured from the 32 kDa form of D1, increased slightly in the dark. The results show that, in the dark, photodamaged D1 is slowly removed upon degradation from the thylakoid membrane and replaced by a de novo synthesized D1 protein. The amount of reaction center proteins and number of photochemically active PSI centers increased in the dark. These results suggest that thylakoid membranes of irradiance-stressed D. salina exist in a state of dynamic flux. We conclude that several aspects of the D. salina recovery from photoinhibition are light independent.
The Treloar—Kearsley instability is studied in the framework of membrane theory. The phenomenon considered is the bifurcation of an equibiaxial stretch of a thin square elastic sheet, in equilibrium under equibiaxial dead loads, to a rectangle at a critical value of the load. The membrane setting, in which the sheet is regarded as an elastic surface, leads to sharper results on the stability of equilibria than those delivered by conventional elasticity theory. Further, definite conclusions can be drawn under weaker constitutive hypotheses. These are illustrated through the use of a particular strain-energy function which renders the analysis nearly trivial.
Of all the herbal pharmacopoeias of the many ancient civilizations, those from China have the longest history and form perhaps the most complex and intricate systems of all forms of empiric medicine. The Chinese pharmacopoeia is a treasure chest of pharmacological products, derived from plants, animals and minerals, which have been used to treat patients for over 5000 yr. In contrast to drugs used in Western medicine, which go through rigorous scientific study before being presented to the public, most of the herbal preparations or animal products used in Chinese medicine were developed by trial and error and have been handed down from physician to student, generation after generation. The enormity of this experience should not be lost on the reader. Thousands of products have been identified that have beneficial effects in thousands of diseases, without the help of the fundamental biochemical and biophysical knowledge and without the benefit of a double-blinded, placebo-controlled study method. Over the entire planet, other ancient civilizations have undergone the same evolution, from the Egyptians, to the Greeks, the Romans, Hindus, and American Indians. All of these cultures have their own collection of pharmaceutical and herbal products used in folklore medicine. Oftentimes, the same plant has been independently identified to work in the same disease states by cultures thousands of miles apart, separated in time by thousands of years, with completely different medical theories and doctrines.
Optically thin AlGaAs/GaAs/AlGaAs double heterostructures, (5000 Å), are floated off their substrates by the epitaxial liftoff technique and mounted on various high reflectivity surfaces. From the absolute photoluminescence intensity, we measure internal and external quantum efficiencies of 99.7% and 72%, respectively. High spontaneous emission quantum efficiency, is important for photon number squeezed light, diode lasers, single-mode light-emitting-diodes, optical interconnects, and solar cells.
