Design of an Active Harmonic Rejection N-Path Filter for Highly Tunable RF Channel Selection

As the number of wireless devices in the world increases, so does the demand for flexible radio receiver architectures capable of operating over a wide range of frequencies and communication protocols. The resonance-based channel-select filters used in traditional radio architectures have a fixed frequency response, making them poorly suited for such a receiver. The N-path filter is based on 1960s technology that has received renewed interest in recent years for its application as a linear high Q filter at radio frequencies. N-path filters use passive mixers to apply a frequency transformation to a baseband low-pass filter in order to achieve a high-Q band-pass response at high frequencies. The clock frequency determines the center frequency of the band-pass filter, which makes the filter highly tunable over a broad frequency range. Issues with harmonic transfer and poor attenuation limit the feasibility of using N-path filters in practice. The goal of this thesis is to design an integrated active N-path filter that improves upon the passive N-path filter’s poor harmonic rejection and limited outof- band attenuation. The integrated circuit (IC) is implemented using the CMRF8SF 130nm CMOS process. The design uses a multi-phase clock generation circuit to implement a harmonic rejection mixer in order to suppress the 3rd and 5th harmonic. The completed active N-path filter has a tuning range of 200MHz to 1GHz and the out-ofband attenuation exceeds 60dB throughout this range. The frequency response exhibits a 14.7dB gain at the center frequency and a -3dB bandwidth of 6.8MHz

Electric-field switchable magnetization via the Dzyaloshinskii-Moriya interaction: FeTiO_3 versus BiFeO_3

In this article we review and discuss a mechanism for coupling between electric polarization and magnetization that can ultimately lead to electric-field switchable magnetization. The basic idea is that a ferroelectric distortion in an antiferromagnetic material can "switch on" the Dzyaloshinskii-Moriya interaction which leads to a canting of the antiferromagnetic sublattice magnetizations, and thus to a net magnetization. This magnetization M is coupled to the polarization P via a trilinear free energy contribution of the form P(M x L), where L is the antiferromagnetic order parameter. In particular, we discuss why such an invariant is present in R3c FeTiO_3 but not in the isostructural multiferroic BiFeO_3. Finally, we construct symmetry groups that in general allow for this kind of ferroelectrically-induced weak ferromagnetism.Comment: 15 pages, 3 images, to appear in J. Phys: Condens. Matter Focus Issue on Multiferroic

Landscape Genetics of Raccoons (\u3ci\u3eProcyon lotor\u3c/i\u3e) Associated with Ridges and Valleys of Pennsylvania: Implications for Oral Rabies Vaccination Programs

Raccoons are the reservoir for the raccoon rabies virus variant in the United States. To combat this threat, oral rabies vaccination (ORV) programs are conducted in many eastern states. To aid in these efforts, the genetic structure of raccoons (Procyon lotor) was assessed in southwestern Pennsylvania to determine if select geographic features (i.e., ridges and valleys) serve as corridors or hindrances to raccoon gene flow (e.g., movement) and, therefore, rabies virus trafficking in this physiographic region. Raccoon DNA samples (n = 185) were collected from one ridge site and two adjacent valleys in southwestern Pennsylvania (Westmoreland, Cambria, Fayette, and Somerset counties). Raccoon genetic structure within and among these study sites was characterized at nine microsatellite loci. Results indicated that there was little population subdivision among any sites sampled. Furthermore, analyses using a model-based clustering approach indicated one essentially panmictic population was present among all the raccoons sampled over a reasonably broad geographic area (e.g., sites up to 36 km apart). However, a signature of isolation by distance was detected, suggesting that widths of ORV zones are critical for success. Combined, these data indicate that geographic features within this landscape influence raccoon gene flow only to a limited extent, suggesting that ridges of this physiographic system will not provide substantial long-term natural barriers to rabies virus trafficking. These results may be of value for future ORV efforts in Pennsylvania and other eastern states with similar landscapes

Targeting of Fumarate Hydratase from Mycobacterium tuberculosis Using Allosteric Inhibitors with a Dimeric-Binding Mode.

With the growing worldwide prevalence of antibiotic-resistant strains of tuberculosis (TB), new targets are urgently required for the development of treatments with novel modes of action. Fumarate hydratase (fumarase), a vulnerable component of the citric acid cycle in Mycobacterium tuberculosis (Mtb), is a metabolic target that could satisfy this unmet demand. A key challenge in the targeting of Mtb fumarase is its similarity to the human homolog, which shares an identical active site. A potential solution to this selectivity problem was previously found in a high-throughput screening hit that binds in a nonconserved allosteric site. In this work, a structure-activity relationship study was carried out with the determination of further structural biology on the lead series, affording derivatives with sub-micromolar inhibition. Further, the screening of this series against Mtb in vitro identified compounds with potent minimum inhibitory concentrations

Investigation of translocation, DNA unwinding, and protein displacement by NS3h, the helicase domain from the Hepatitis C virus helicase

Helicases are motor proteins that are involved in DNA and RNA metabolism, replication, recombination, transcription and repair. The motors are powered by ATP binding and hydrolysis. Hepatitis C virus encodes a helicase called non-structural protein (NS3). NS3 possesses protease and helicase activities on its N-terminal and C-terminal domains respectively. The helicase domain of NS3 protein is referred as NS3h. In vitro, NS3h catalyzes RNA and DNA unwinding in a 3’ to -5’ direction. The directionality for unwinding is thought to arise in part from the enzyme's ability to translocate along DNA, but translocation has not been shown explicitly. We examined the DNA translocase activity of NS3h by using single-stranded oligonucleotide substrates containing a fluorescent probe on the 5’ end. NS3h can bind to the ssDNA and in the presence of ATP, move towards the 5’-end. When the enzyme encounters the fluorescent probe, a fluorescence change is observed that allows translocation to be characterized. Under conditions that favor binding of one NS3h per DNA substrate (100 nM NS3h, 200 nM oligonucleotide) we find that NS3h translocates on ssDNA at a rate of 46 ± 5 nt s−1 and that it can move for 230 ± 60 nt before dissociating from the DNA. The translocase activity of some helicases is responsible for displacing proteins that are bound to DNA. We studied protein displacement by using a ssDNA oligonucleotide covalently linked to biotin on the 5’-end. Upon addition of streptavidin, a ‘protein-block’ was placed in the pathway of the helicase. Interestingly, NS3h was unable to displace streptavidin from the end of the oligonucleotide, despite its ability to translocate along the DNA. The DNA unwinding activity of NS3h was examined using a 22 bp duplex DNA substrate under conditions that were identical to those used to study translocation. NS3h exhibited little or no DNA unwinding under single cycle conditions, supporting the conclusion that NS3h is a relatively poor helicase in its monomeric form, as has been reported. In summary, NS3h translocates on ssDNA as a monomer, but the translocase activity does not correspond to comparable DNA unwinding activity or protein-displacement activity under identical conditions

New criteria for the molecular identification of cereal grains associated with archaeological artefacts.

The domestication and transmission of cereals is one of the most fundamental components of early farming, but direct evidence of their use in early culinary practices and economies has remained frustratingly elusive. Using analysis of a well-preserved Early Bronze Age wooden container from Switzerland, we propose novel criteria for the identification of cereal residues. Using gas chromatography mass spectrometry (GC-MS), we identified compounds typically associated with plant products, including a series of phenolic lipids (alkylresorcinols) found only at appreciable concentration in wheat and rye bran. The value of these lipids as cereal grain biomarkers were independently corroborated by the presence of macrobotanical remains embedded in the deposit, and wheat and rye endosperm peptides extracted from residue. These findings demonstrate the utility of a lipid-based biomarker for wheat and rye bran and offer a methodological template for future investigations of wider range of archaeological contexts. Alkylresorcinols provide a new tool for residue analysis which can help explore the spread and exploitation of cereal grains, a fundamental component of the advent and spread of farming

Default Risk and Equity Returns: A Comparison of the Bank-Based German and the U.S. Financial System

In this paper, we address the question whether the impact of default risk on equity returns depends on the financial system firms operate in. Using an implementation of Merton's option-pricing model for the value of equity to estimate firms' default risk, we construct a factor that measures the excess return of firms with low default risk over firms with high default risk. We then compare results from asset pricing tests for the German and the U.S. stock markets. Since Germany is the prime example of a bank-based financial system, where debt is supposedly a major instrument of corporate governance, we expect that a systematic default risk effect on equity returns should be more pronounced for German rather than U.S. firms. Our evidence suggests that a higher firm default risk systematically leads to lower returns in both capital markets. This contradicts some previous results for the U.S. by Vassalou/Xing (2004), but we show that their default risk factor looses its explanatory power if one includes a default risk factor measured as a factor mimicking portfolio. It further turns out that the composition of corporate debt affects equity returns in Germany. Firms' default risk sensitivities are attenuated the more a firm depends on bank debt financing

FK 506 pre-treatment is associated with reduced levels of tumor necrosis factor and interleukin 6 following hepatic ischemia/reperfusion

Using a rat model, the effect of pre-treatment with FK 506 on hepatic ischemia/reperfusion injury was investigated. All control animals died within 72 h of the ischemia/reperfusion injury. Pre-treatment of the animals with FK 506 (0.3 mg/kg in 0.5 ml saline) administered intravenously improved survival. The most striking protection against fatal ischemia/reperfusion injury was achieved in rats that were given FK 506 6 and 24 h prior to the induction of the hepatic ischemic insult (70% and 80% 10-day survival rates, respectively). The hepatoprotective effect of FK 506 was assessed further in a second experiment in which the serum levels of tumor necrosis factor (TNF) and interleukin 6 (IL-6) were measured. These results suggest that a 60-min period of hepatic ischemia and subsequent reperfusion triggers the release of both TNF and IL-6, and that FK 506 pre-treatment (6 h before the ischemic episode) significantly inhibits the production and/or release of these two cytokines compared to untreated controls. These data provide additional information concerning the immunosuppressive and hepatoprotective activities of FK 506. Based upon these data, it is probable that FK 506 attenuates hepatic ischemia/reperfusion injury, at least in part, by reducing TNF and IL-6 levels. © 1993 Elsevier Scientific Publishers Ireland Ltd. All rights reserved