Peroxyacetic Acid Delignification of Wood and Bark from Ponderosa Pine (Pinus ponderosa)

Ruminant species, which include cattle, sheep and goats, have the unique capability of digesting. cellulose and hemicellulose, the cell-wall carbohydrates that constitute 70 to 80 percent of wood fiber. By their conversion of these higher polysaccharides, which are indigestible by humans and other monogastrics, to animal products the ruminant species offer a potential means for solving the residue disposal problems of the wood industry while concomitantly extending the food supply for human nutrition. The ability of ruminants to digest the cell-wall carbohydrates depends on the microbial digestion that occurs in the reticule-rumen. This organ lies between the esophagus and the abomasum or true stomach and contains large numbers of bacterial and protozoal organisms in an anaerobic atmosphere. Many of these microorganisms possess enzyme systems which are capable of hydrolyzing the beta configuration of the glycosidic linkages which join the monomeric subunits of cellulose and hemicellulose. Through this process of enzymatic hydrolysis cellulose and hemicellulose are gradually degraded to their basic sugar units which are further metabolized to volatile fatty acids, primarily acetic and propionic. These fatty acids are absorbed through the reticule-rumen wall and serve as the main source of energy to the animal. As a potential food source wood has several advantages. It is one of the few renewable resources that is available in abundant supply and can be obtained year-round. Because its growth occurs slowly over a period of many years short term fluctuations in supply are not likely to be a problem. Its ability to grow on land area that is not well suited for human habitation or domestic crop cultivation makes it very noncompetitive for land use. Many researchers have investigated the inclusion of raw wood fiber into ruminant rations and numerous physical and chemical treatments have been conducted in attempts to improve its nutritional quality. In spite of these efforts a desirable processing technique has yet to be achieved. One of the major limitations is the nature of the raw material itself. Wood is a heterogeneous substance that varies in physical and chemical composition among genera and species. Within a single tree, composition varies cross-sectionally and longitudinally and is influenced by seasonal changes. This investigation will review previous work concerning the use of wood fiber as a ruminant feed and will evaluate the effectiveness of peroxyacetic acid treatment of wood fibers to improve their digestibility

Superconductivity in CeCoIn5-xSnx: Veil Over an Ordered State or Novel Quantum Critical Point?

Measurements of specific heat and electrical resistivity in magnetic fields up to 9 T along [001] and temperatures down to 50 mK of Sn-substituted CeCoIn5 are reported. The maximal -ln(T) divergence of the specific heat at the upper critical field H_{c2} down to the lowest temperature characteristic of non-Fermi liquid systems at the quantum critical point (QCP), the universal scaling of the Sommerfeld coefficient, and agreement of the data with spin-fluctuation theory, provide strong evidence for quantum criticality at H_{c2} for all x < 0.12 in CeCoIn5-xSnx. These results indicate the "accidental" coincidence of the QCP located near H_{c2} in pure CeCoIn5, in actuality, constitute a novel quantum critical point associated with unconventional superconductivity.Comment: 12 pages, 4 figure

Hyperfine Interactions in the Heavy Fermion CeMIn_5 Systems

The CeMIn_5 heavy fermion compounds have attracted enormous interest since their discovery six years ago. These materials exhibit a rich spectrum of unusual correlated electron behavior, and may be an ideal model for the high temperature superconductors. As many of these systems are either antiferromagnets, or lie close to an antiferromagnetic phase boundary, it is crucial to understand the behavior of the dynamic and static magnetism. Since neutron scattering is difficult in these materials, often the primary source of information about the magnetic fluctuations is Nuclear Magnetic Resonance (NMR). Therefore, it is crucial to have a detailed understanding of how the nuclear moments interact with conduction electrons and the local moments present in these systems. Here we present a detailed analysis of the hyperfine coupling based on anisotropic hyperfine coupling tensors between nuclear moments and local moments. Because the couplings are symmetric with respect to bond axes rather than crystal lattice directions, the nuclear sites can experience non-vanishing hyperfine fields even in high symmetry sites.Comment: 15 pages, 5 figure

Determining the underlying Fermi surface of strongly correlated superconductors

The notion of a Fermi surface (FS) is one of the most ingenious concepts developed by solid state physicists during the past century. It plays a central role in our understanding of interacting electron systems. Extraordinary efforts have been undertaken, both by experiment and by theory, to reveal the FS of the high temperature superconductors (HTSC), the most prominent strongly correlated superconductors. Here, we discuss some of the prevalent methods used to determine the FS and show that they lead generally to erroneous results close to half filling and at low temperatures, due to the large superconducting gap (pseudogap) below (above) the superconducting transition temperature. Our findings provide a perspective on the interplay between strong correlations and superconductivity and highlight the importance of strong coupling theories for the characterization as well as the determination of the underlying FS in ARPES experiments

Heat Transport as a Probe of Electron Scattering by Spin Fluctuations: the Case of Antiferromagnetic CeRhIn5

Heat and charge conduction were measured in the heavy-fermion metal CeRhIn5, an antiferromagnet with T_N=3.8 K. The thermal resistivity is found to be proportional to the magnetic entropy, revealing that spin fluctuations are as effective in scattering electrons as they are in disordering local moments. The electrical resistivity, governed by a q^2 weighting of fluctuations, increases monotonically with temperature. In contrast, the difference between thermal and electrical resistivities, characterized by an omega^2 weighting, peaks sharply at T_N and eventually goes to zero at a temperature T^* ~ 8 K. T^* thus emerges as a measure of the characteristic energy of magnetic fluctuations.Comment: 4 pages, 4 figure

Magnetic Excitations of the 2-D Sm Spin Layers in Sm(La,Sr)CuO4

We present specific heat and susceptibility data on Sm(La,Sr)CuO4 in magnetic fields up to 9 T and temperatures down to 100 mK. We find a broad peak in specific heat which is insensitive to magnetic field at a temperature of 1.5 K with a value of 2.65 J/mol K. The magnetic susceptibility at 5 T continues to increase down to 2 K, the lowest temperature measured. The data suggest that the Sm spin system may be an ideal realization of the frustrated Heisenberg antiferromagnet on the square lattice.Comment: 2 pages, 2 figures, submitted to IC

Non-Fermi Liquid behavior in CeIrIn5_5 near a metamagnetic transition

We present specific heat and resistivity study of CeIrIn5 in magnetic fields up to 17 T and temperature down to 50 mK. Both quantities were measured with the magnetic field parallel to the c-axis (H || [001]) and within the a-b plane (H \perp [001]). Non-Fermi-liquid (NFL) behavior develops above 12 T for H || [001]. The Fermi liquid state is much more robust for H \perp [001] and is suppressed only moderately at the highest applied field. Based on the observed trends and the proximity to a metamagnetic phase transition, which exists at fields above 25 T for H || [001], we suggest that the observed NFL behavior in CeIrIn5 is a consequence of a metamagnetic quantum critical point.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Letter