A Note on the Oil Price Trend and GARCH Shocks

This paper investigates the trend in the monthly real price of oil between 1990 and 2008 with a generalized autoregressive conditional heteroskedasticity (GARCH) model. Trend and volatility are estimated jointly with the maximum likelihood estimation. There is long persistence in the variance of oil price shocks, and a GARCH unit root (GUR) test can potentially yield a significant power gain relative to the augmented Dickey-Fuller (ADF) test. After allowing for nonlinearity, the evidence supports a deterministic trend in the price of oil. The deterministic trend implies that influence of a price shock is transitory and policy efforts to restore a predictable price after a shock would be unwarranted in the long run.Oil Price, Volatility, Trend, GARCH, Fourier Form

An Intermediate State of the {gamma}-Aminobutyric Acid Transporter GAT1 Revealed by Simultaneous Voltage Clamp and Fluorescence

The rat {gamma}-aminobutyric acid transporter GAT1 expressed in Xenopus oocytes was labeled at Cys74, and at one or more other sites, by tetramethylrhodamine-5-maleimide, without significantly altering GAT1 function. Voltage-jump relaxation analysis showed that fluorescence increased slightly and monotonically with hyperpolarization; the fluorescence at -140 mV was ~0.8% greater than at +60 mV. The time course of the fluorescence relaxations was mostly described by a single exponential with voltage-dependent but history-independent time constants ranging from ~20 ms at +60 mV to ~150 ms at -140 mV. The fluorescence did not saturate at the most negative potentials tested, and the midpoint of the fluorescence–voltage relation was at least 50 mV more negative than the midpoint of the charge–voltage relation previously identified with Na+ binding to GAT1. The presence of {gamma}-aminobutyric acid did not noticeably affect the fluorescence waveforms. The fluorescence signal depended on Na+ concentration with a Hill coefficient approaching 2. Increasing Cl- concentration modestly increased and accelerated the fluorescence relaxations for hyperpolarizing jumps. The fluorescence change was blocked by the GAT1 inhibitor, NO-711. For the W68L mutant of GAT1, the fluorescence relaxations occurred only during jumps to high positive potentials, in agreement with previous suggestions that this mutant is trapped in one conformational state except at these potentials. These observations suggest that the fluorescence signals monitor a novel state of GAT1, intermediate between the E*out and Eout states of Hilgemann, D.W., and C.-C. Lu (1999. J. Gen. Physiol. 114:459–476). Therefore, the study provides verification that conformational changes occur during GAT1 function

Cyclic nucleotide-gated channels: structural basis of ligand efficacy and allosteric modulation

Most working proteins, including metabolic enzymes, transcription regulators, and membrane receptors, transporters, and ion channels, share the property of allosteric coupling. The term 'allosteric' means that these proteins mediate indirect interactions between sites that are physically separated on the protein. In the example of ligand-gated ion channels, the binding of a suitable ligand elicits local conformational changes at the binding site, which are coupled to further conformational changes in regions distant from the binding site. The physical motions finally arrive at the site of biological activity: the ion-permeating pore. The conformational changes that lead from the ligand binding to the actual opening of the pore comprise 'gating'. In 1956, del Castillo and Katz suggested that the competition between different ligands at nicotinic acetylcholine receptors (nAChRs) could be explained by formation of an intermediate, ligand-bound, yet inactive state of the receptor, which separates the active state of the receptor from the initial binding of the ligand (del Castillo & Katz, 1957). This 'binding-then-gating', two-step model went beyond the then-prevailing drug-receptor model that assumes a single bimolecular binding reaction, and paralleled Stephenson's conceptual dichotomy of 'affinity' and 'efficacy' (Stephenson, 1956). In 1965 Monod, Wyman and Changeux presented a simple allosteric model (the MWC model) (Monod et al. 1965) that explained the cooperative binding of oxygen to haemoglobin; it was adopted as an important paradigm for ligand-gated channels soon after its initial formulation (Changeux et al. 1967; Karlin, 1967; Colquhoun, 1973)

Optofluidic circular grating distributed feedback dye laser

We demonstrate an optically pumped surface emitting optofluidic dye laser using a second-order circular grating distributed feedback resonator. We present a composite bilayer soft lithography technique specifically developed for the fabrication of our dye laser and investigate a hybrid polymer material system [poly(dimethylsiloxane)/perfluoropolyether] to construct high-resolution Bragg gratings. Our lasers emit single frequency light at low lasing thresholds of 6 µJ/mm^2. These optofluidic dye lasers can serve as low-cost and compact coherent light sources that are fully integrated within microfluidic analysis chips and provide an efficient approach to construct compact spectroscopy systems