High-efficiency low-voltage-stress Class-EF PA with extended maximum operating frequency

The Class-EF power amplifier (PA) introduced recently has a peak switch voltage much lower than the well-known Class-E PA. However, the value of the transistor output capacitance at high frequencies is typically larger than the required Class-EF optimum shunt capacitance. As a result, softswitching operation that minimizes power dissipation during OFF-to-ON transient cannot be achieved at high frequencies. A novel Class-EF topology with transmission-line load network proposed in this paper allows the PA to operate at much higher frequencies without trading the other figures of merit. Closed-form formulations are derived to simultaneously satisfy the Class-EF impedances requirement at fundamental frequency, all even harmonics, and the first two odd harmonics as well as to provide matching to 50O load. © 2011 Institut fur Mikrowellen.

Human aflatoxin albumin adducts quantitatively compared by ELISA, HPLC with fluorescence detection, and HPLC with isotope dilution mass spectrometry

Essential to the conduct of epidemiologic studies examining aflatoxin exposure and the risk of heptocellular carcinoma, impaired growth, and acute toxicity has been the development of quantitative biomarkers of exposure to aflatoxins, particularly aflatoxin B-1. In this study, identical serum sample sets were analyzed for aflatoxin-albumin adducts by ELISA, high-performance liquid chromatography (HPLC) with fluorescence detection (HPLC-f), and HPLC with isotope dilution mass spectrometry (IDMS). The human samples analyzed were from an acute aflatoxicosis outbreak in Kenya in 2004 (n = 102) and the measured values ranged from 0.018 to 67.0, nondetectable to 13.6, and 0.002 to 17.7 ng/mg albumin for the respective methods. The Deming regression slopes for the HPLC-f and ELISA concentrations as a function of the IDMS concentrations were 0.71 (r(2) = 0.95) and 3.3 (r(2) = 0.96), respectively. When the samples were classified as cases or controls, based on clinical diagnosis, all methods were predictive of outcome (P < 0.01). Further, to evaluate assay precision, duplicate samples were prepared at three levels by dilution of an exposed human sample and were analyzed on three separate days. Excluding one assay value by ELISA and one assay by HPLC-f, the overall relative SD were 8.7%, 10.5%, and 9.4% for IDMS, HPLC-f, and ELISA, respectively. IDMS was the most sensitive technique and HPLC-f was the least sensitive method. Overall, this study shows an excellent correlation between three independent methodologies conducted in different laboratories and supports the validation of these technologies for assessment of human exposure to this environmental toxin and carcinogen.

Tip-enhanced fluorescence imaging of quantum dots

We have imaged the fluorescence from a single quantum dot cluster using an apertureless scanning near-field optical microscope. When a sharp gold tip is brought within a few nanometers from the sample surface, the resulting enhancement in quantum dot fluorescence in the vicinity of the tip leads to a resolution of about 60 nm. We determine this enhancement of the fluorescence to be about fourfold in magnitude, which is consistent with the value expected as a result of competition between fluorescence quenching and electromagnetic field enhancement. (C) 2005 American Institute of Physics.

Fluorescence enhancement and energy transfer in apertureless scanning near-field optical microscopy

We investigate the mechanisms for fluorescence enhancement and energy transfer near a gold tip in apertureless scanning near-field optical microscopy. Using a simple quasi-static model, we show that the observed enhancement of fluorescence results from competition between enhancement and quenching, and is dependent on a range of experimental parameters. We find good qualitative agreement with the results of measurements of the effect of both sharp and blunt tips on quantum dot fluorescence, and provide a demonstration of tip-enhanced fluorescence imaging with 60 nm resolution.

Abnormal changes in voltage-gated sodium channels NaV1.1, NaV1.2, NaV1.3, NaV1.6 and in Calmodulin/calmodulin-dependent protein kinase II, within the brains of spontaneously epileptic rats and tremor rats

Voltage-gated sodium channels (VGSCs) play a crucial role in epilepsy. The expressions of different VGSCs subtypes are varied in diverse animal models of epilepsy that may reflect their multiple phenotypes or the complexity of the mechanisms of epilepsy. In a previous study, we reported that NaV1.1 and NaV1.3 were up-regulated in the hippocampus of the spontaneously epileptic rat (SER). In this study, we further analyzed both the expression and distribution of the typical VGSC subtypes NaV1.1, NaV1.2, NaV1.3 and NaV1.6 in the hippocampus and in the cortex of the temporal lobe of two genetic epileptic animal models: the SER and the tremor rat (TRM). The expressions of calmodulin (CaM) and calmodulin-dependent protein kinase II (CaMKII) were also analyzed with the purpose of assessing the effect of the CaM/CaMKII pathway in these two models of epilepsy. Increased expression of the four VGSC subtypes and CaM, accompanied by a decrease in CaMKII was observed in the hippocampus of both the SERs and the TRM rats. However, the changes observed in the expression of VGSC subtypes and CaM were decreased with an elevated CaMKII in the cortex of their temporal lobes. Double-labeled immunofluorescence data suggested that in SERs and TRM rats, the four subtypes of the VGSC proteins were present throughout the CA1, CA3 and dentate gyrus regions of the hippocampus and temporal lobe cortex and these were co-localized in neurons with CaM. These data represent the first evidence of abnormal changes in expression of four VGSC subtypes (NaV1.1, NaV1.2, NaV1.3 and NaV1.6) and CaM/CaMKII in the hippocampus and temporal lobe cortex of SERs and TRM rats. These changes may be involved in the generation of epileptiform activity and underlie the observed seizure phenotype in these rat models of genetic epilepsy.

Serological responses to experimental Norwalk virus infection measured using a quantitative duplex time-resolved fluorescence immunoassay

A quantitative duplex time-resolved fluorescence assay, dissociation-enhanced lanthanide fluorescent immunoassay (DELFIA), was developed to measure Norwalk virus (NV)-specific IgA and IgG antibodies simultaneously. The duplex assay showed superior performance by detecting seroconversion following experimental NV infection at an earlier time point than a reference total immunoglobulin enzyme-linked immunosorbent assay (ELISA).

Gold Nanoparticles-Coated SU-8 for Sensitive Fluorescence-Based Detections of DNA

SU-8 epoxy-based negative photoresist has been extensively employed as a structural material for fabrication of numerous biological microelectro-mechanical systems (Bio-MEMS) or lab-on-a-chip (LOC) devices. However, SU-8 has a high autofluorescence level that limits sensitivity of microdevices that use fluorescence as the predominant detection workhorse. Here, we show that deposition of a thin gold nanoparticles layer onto the SU-8 surface significantly reduces the autofluorescence of the coated SU-8 surface by as much as 81% compared to bare SU-8. Furthermore, DNA probes can easily be immobilized on the Au surface with high thermal stability. These improvements enabled sensitive DNA detection by simple DNA hybridization down to 1 nM (a two orders of magnitude improvement) or by solid-phase PCR with sub-picomolar sensitivity. The approach is simple and easy to perform, making it suitable for various Bio-MEMs and LOC devices that use SU-8 as a structural material.

Coexpressing shRNA with fluorescence tags for quantification of cell migration studies

Understanding migration of cells has many implications in human physiology; some examples include developmental biology, healing, immune responses and tissue remodeling. On the other hand, invasive migration by tumor cells is pathological and is a major cause of mortality amongst cancer sufferers. Cell migration assays have been widely used to quantify potentially metastatic genes. In recent years, the use of RNAi has significantly increased the tools available in cell migration research due to its specific gene targeting for knockdown. The inability to ensure 100% transfection/transduction efficiency reduces the sensitivity of cell migration assays because cells not successfully transfected/transduced with the RNAi are also included in the calculations. This study introduces a different experimental setup mathematically expressed in our named normalized relative infected cell count (N-RICC) that analyses cell migration assays by co-expressing retrovirally transduced shRNA with fluorescence tags from a single vector. Vectors transduced into cells are visible under fluorescence, thus alleviating the problems involved with transduction efficiency by individually identifying cells with targeted genes. Designed shRNAs were targeted against a list of potentially metastatic genes in a highly migratory breast cancer cell line model, MDA-MB-231. We have successfully applied N-RICC analysis to show greater sensitivity of integrin alpha5 (ITGA5) and Ras homologue A (RhoA) in cell metastasis over conventional methods in scratch-wound assays and migration chambers assays.

Clinical and technical factors associated with skin intrinsic fluorescence in subjects with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study

The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications(EDIC) studies have established multiyear mean hemoglobin A1c (HbA1c) as predictive of microvascular complications in persons with type 1 diabetes. However, multiyear mean HbA1c is not always available in the clinical setting. Skin advanced glycation end products (AGEs) are thought to partially reflect effects of hyperglycemia over time, and measurement of skin AGEs might be a surrogate for multiyear mean HbA1c. As certain AGEs fluoresce and skin fluorescence has been demonstrated to correlate with the concentration of skin AGEs, noninvasive measurement by skin intrinsic fluorescence(SIF) facilitates the exploration of the association of mean HbA1c and other clinical/technical factors with SIF using the detailed phenotypic database available in DCCT/EDIC.

The Association of Skin-Intrinsic Fluorescence With Type 1 Diabetes Complications in the DCCT/EDIC Study

OBJECTIVESTo determine whether skin-intrinsic fluorescence (SIF) is associated with long-term complications of type 1 diabetes (T1D) and, if so, whether it is independent of chronic glycemic exposure and previous intensive therapy.RESEARCH DESIGN AND METHODSWe studied 1,185 (92%) of 1,289 active Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) participants from 2010 to 2011. SIF was determined using a fluorescence spectrometer and related cross-sectionally to recently determined measures of retinopathy (stereo fundus photography), cardiac autonomic neuropathy (CAN; R-R interval), confirmed clinical neuropathy, nephropathy (albumin excretion rate [AER]), and coronary artery calcification (CAC).RESULTSOverall, moderately strong associations were seen with all complications, before adjustment for mean HbA1c over time, which rendered these associations nonsignificant with the exception of sustained AER >30 mg/24 h and CAC, which were largely unaffected by adjustment. However, when examined within the former DCCT treatment group, associations were generally weaker in the intensive group and nonsignificant after adjustment, while in the conventional group, associations remained significant for CAN, sustained AER >30 mg/24 h, and CAC even after mean HbA1c adjustment.CONCLUSIONSSIF is associated with T1D complications in DCCT\EDIC. Much of this association appears to be related to historical glycemic exposure, particularly in the previously intensively treated participants, in whom adjustment for HbA1c eliminates statistical significance.

Voltage Sensing Using an Asynchronous Charge-to-Digital Converter for Energy-Autonomous Environments

In future systems with relatively unreliable and unpredictable energy sources such as harvesters, the system power supply may become non-deterministic. For energy effective operations, Vdd is an important parameter in any meaningful system control mechanism. Reliable and accurate on-chip voltage sensors are therefore indispensible for the power and computation management of such systems. Existing voltage sensing methods are not suitable because they usually require a stable and known reference (voltage, current, time, frequency, etc.), which is difficult to obtain in this environment. This paper describes an autonomous reference-free voltage sensor designed using an asynchronous counter powered by the charge on a capacitor and a small controller. Unlike existing methods, the voltage information is directly generated as a digital code. The sensor, fabricated in the 180 nm technology node, was tested successfully through performing measurements over the voltage range from 1.8 V down to 0.8 V.

Capability Curve Based Enhanced Reactive Power Control Strategy for Stability Enhancement and Network Voltage Management

Reactive power has become a vital resource in modern electricity networks due to increased penetration of distributed generation. This paper examines the extended reactive power capability of DFIGs to improve network stability and capability to manage network voltage profile during transient faults and dynamic operating conditions. A coordinated reactive power controller is designed by considering the reactive power capabilities of the rotor-side converter (RSC) and the grid-side converter (GSC) of the DFIG in order to maximise the reactive power support from DFIGs. The study has illustrated that, a significant reactive power contribution can be obtained from partially loaded DFIG wind farms for stability enhancement by using the proposed capability curve based reactive power controller; hence DFIG wind farms can function as vital dynamic reactive power resources for power utilities without commissioning additional dynamic reactive power devices. Several network adaptive droop control schemes are also proposed for network voltage management and their performance has been investigated during variable wind conditions. Furthermore, the influence of reactive power capability on network adaptive droop control strategies has been investigated and it has also been shown that enhanced reactive power capability of DFIGs can substantially improve the voltage control performance.

Fluorescent switches with high selectivity towards sodium ions:Correlation of ion-induced conformation switching with fluorescence function

Diazacoronand 2 undergoes drastic conformational switching upon binding sodium ions as demonstrated by solution- and solid-state studies, which permit the design of efficient fluorescent PET (photoinduced electron transfer) switches 3a,b.