FT Values Research Articles

Gender, Age, Puberty, and BMI Related Changes of TSH and Thyroid Hormones in Schoolchildren Living in a Long-standing Iodine Replete Area

The aim of the work was to assess thyroid function in children and adolescents in an iodine replete area and to explore possible effects of age, gender, puberty, and adiposity. Thyrotropin (TSH), total triiodothyronine (T (3)), total thyroxine (T (4)), free thyroxine (FT (4)), and the T (4)/T (3) ratio were determined for 440 schoolchildren (200 boys and 240 girls), aged 5-18 years, living in an iodine replete region. Body Mass Index (BMI), BMI standard deviation score (BMI-SDS), and Body Surface Area (BSA) were calculated. In girls there was a negative correlation of TSH, T (3), and FT (4) values with age. In boys there was a negative correlation only of T (3) values with age. Girls had lower TSH, T (4), and T (3) values, whereas boys had only lower T (3) values at puberty compared to the prepubertal stage. Girls had lower TSH values than boys (p<0.03) only at puberty. BMI-SDS in boys and girls were 0.21 and 0.03, respectively. BMI-SDS was not related to TSH, T (4), or T (3) in either gender, whereas it was negatively related to T (4)/T (3) ratio in boys and to FT (4) in girls. We conclude that estrogens may exert a suppressive effect on the pituitary-thyroid axis after puberty. TSH values are not correlated with BMI-SDS, whereas T (4)/T (3) ratio in boys and FT (4) in girls are negatively correlated with BMI-SDS.

Studies on the Physicochemical Properties and Existence of Water Products (as Drinks) Advertised as Having Smaller Cluster Sizes of H2O Molecules than Those of Regular Water

The in vitro physicochemical properties of 6 bottled water products (as drinks), advertised as having cluster sizes of H2O molecules smaller than those of regular water, were studied. No significant differences in the boiling temperature (BT, near 100°C) or freezing temperature (FT, near 0°C) were observed between all 8 aqueous solutions examined, including deionized water (DW) and tap water as controls, although DW had the lowest mean BT and highest mean FT values. The specific gravity of all the examined aqueous solutions, including the controls, changed in a temperature-dependently manner, showing the greatest value (near 1.000) at 4°C. Analyses of inorganic components revealed that various mineral components were dissolved in aqueous solutions examined other than DW, suggesting that the trends of the lowest BT and highest FT for the DW control were due to the absence of these solutes. These results did not demonstrate the presence of an abnormality in the hydrogen bonds between H2O molecules in the sample solutions compared to the controls. In other words, the claims by the manufacturers in their advertisements concerning the cluster sizes of H2O molecules for their water products were not confirmed by the findings of this study.

Changes in dental caries in Zurich school-children over a period of 45 years.

In 16 rural communities of the Canton of Zurich, school-children of all age groups participated in dental examinations conducted at intervals of 4 years since 1963/64. The same standardised method was used throughout the entire period. This study documents the caries experience over a period of 45 years. From 1964 to 2009, the DM*FT per 14-year-old child fell from 12.50 to 1.31, corresponding to a caries reduction of 90%. The caries experience in 8-, 10- and 12-year-olds decreased by 90% to 92%. From 1964 to 2009, the "Significant Caries Index" (the mean DM*FT in the third of 12-year-olds with the highest DM*FT values) fell from 13.09 to 2.20, corresponding to a caries reduction of 83%. The observed caries decline was unexpectedly high. The effect of fluorides may explain a caries reduction of roughly 50%. A large part of the decline, however, remains unexplained. Possible causes are discussed in this paper.

A mechanomyographic frequency-based fatigue threshold test

Theoretically, the mechanomyographic (MMG) mean power frequency fatigue threshold (MMG MPF FT) describes the maximal isometric torque that can be maintained for an extended period of time with no change in the global firing rate of the unfused, activated motor units. Purpose The purposes of this study were twofold: (1) to determine if the mathematical model for estimating the electromyographic (EMG) MPF FT from the frequency of the EMG signal was applicable to the frequency domain of the MMG signal to estimate a new fatigue threshold called the MMG MPF FT; and (2) to compare the mean torque levels derived from the MMG MPF FT test for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during isometric leg extension muscle actions. Methods Nine adults (4 men and 5 women; mean ± S.D. age = 21.6 ± 1.2 years) performed three or four continuous, fatiguing, isometric muscle actions of the leg extensors at 30, 45, 60, and 75% of maximum voluntary isometric contraction (MVIC) to exhaustion. Surface MMG signals were recorded from the VL, VM, and RF muscles during each fatiguing isometric muscle action. The MMG MPF FT was defined as the y-intercept of the isometric torque versus slope coefficient (MMG MPF versus time) plot. Results There were no significant differences among the MMG MPF FT values for the VL, VM, and RF (34.8 ± 23.4, 32.1 ± 16.1, and 31.6 ± 15.2 N m, respectively) muscles. Conclusion The MMG MPF FT test may provide a non-invasive method to examine the effects of various interventions on the global motor unit firing rate during isometric muscle actions.

Non-thyroidal illness syndrome and short-term survival in a hospitalised older population

non-thyroidal illness syndrome (NTIS) has been associated with an adverse clinical outcome. to evaluate the prevalence of NTIS, its impact on patients' survival and the possible pathogenic role of systemic inflammation. observational cross-sectional analysis. three hundred and one acutely ill older patients (156 women; median age 81 years, range 65-101) consecutively admitted to a primary care unit. serum FT(3), FT(4) and thyrotropin levels as well as acute inflammation indexes were evaluated. the NTIS prevalence (specifically low T3 syndrome) was 31.9%. A significant association was found between NTIS and acute renal failure (P = 0.006), New York Heart Association classification (NYHA) IV heart failure (P = 0.003) and metastasised cancer disease (P = 0.0002). Serum FT(3) values correlated inversely with serum C-reactive protein (P < 0.0001), lactate dehydrogenase (P = 0.0004), fibrinogen (P = 0.03) and erythrocyte sedimentation rate (P < 0.0001) values, and progressively decreased with increasing tertiles of age (P = 0.0004). The mortality rate was significantly higher (P = 0.0002) among patients with low T3 syndrome, which emerged as the sole predictive factor of death (odds ratio 4.3; 95% confidence interval 1.7-10.5). low T3 syndrome is very common in the hospitalised older population, emerging as the most sensitive independent predictor of short-term survival. Serum FT(3) determination should be included in the assessment of short-term prognosis of acutely ill older patients.

Thyroid disorders in women of Puducherry

Thyroid stimulating hormone (TSH), Free Thyroxine (FT(4)) and Free Triiodothyronine (FT(3)) were assayed in 505 women of this region. 60 women had previous history of thyroid disease. The remaining 445 women formed the "Disease free group". A "Reference group" was obtained by excluding women with previous and present history of thyroid dysfunction. Of the total 505 women examined 15.8% had thyroid dysfunction and 84.2% were euthyroid. 11.5% were hypothyroid (9.5% sub-clinical) and 1.8% hyperthyroid (1.2% clinical). The geometric mean TSH for the total population was 2.65 μIU/ml. It was significantly (p=0.025) lower in the reference population 2.17 μIU/ml. There was no significant difference in the FT(3) and FT(4) values between groups. 19% of women over 60 years had elevated TSH above 4.5 μIU/ml. The 2.5 and 97.5 percentiles of the reference population was 1.1-5.2 μIU/ml. 6.1% of women in the reference group had TSH levels above the reference intervals. Hypothyroidism particularly sub-clinical hypothyroidism is predominantly present amongst women in this iodine sufficient region. Evaluation of thyroid status could help in early detection and treatment.

Mapping the Zonal Organization of Tumor Perfusion and Permeability in a Rat Glioma Model by Using Dynamic Contrast-enhanced Synchrotron Radiation CT

To depict and analyze in vivo the tumor zone organization of C6 gliomas depicted on quantitative parametric maps obtained with dynamic contrast material-enhanced synchrotron radiation computed tomography (CT) in a tightly controlled data-processing protocol. Animal use was compliant with official French guidelines and was assessed by the local Internal Evaluation Committee for Animal Welfare and Rights. Fifteen Wistar rats with orthotopically implanted gliomas were studied at monochromatic synchrotron radiation CT after receiving a bolus injection of contrast material. The iodine concentration maps were analyzed by using a compartmental model selected from among a package of models. Choice of model and assessment of the relevance of the model were guided by quality criteria. Tissue blood flow (F(T)), tissue blood volume fraction (V(T)), permeability-surface area product (PS), artery-to-tissue delay (D(A-T)), and vascular mean transit time (MTT) maps were obtained. Parametric map findings were compared with histologic findings. Local regions of interest were selected in the contralateral hemisphere and in several tumor structures to characterize the tumor microvasculature. Differences in parameter values between regions were assessed with the Wilcoxon method. Whole-tumor parameters were expressed as means +/- standard errors of the mean: Mean F(T), V(T), PS, and D(A-T) values and MTT were 61.4 mL/min/100 mL +/- 15.3, 2.4% +/- 0.4, 0.37 mL/min/100 mL +/- 0.11, 0.24 second +/- 0.06; and 3.9 seconds +/- 0.83, respectively. MTT and mean PS were significantly lower (P < .01) in the normal contralateral tissue: 1.10 seconds +/- 0.06 and < or = 10(-5) mL/min/100 mL, respectively. Tumor regions were characterized by significantly different (P < .05) F(T) and V(T) pairs: 108 mL/min/100 mL and 3.66%, respectively, at the periphery; 45.9 mL/min/100 mL and 1.91%, respectively, in the intermediate zone; 5.1 mL/min/100 mL and 0.42%, respectively, in the center; and 210 mL/min/100 mL and 6.82%, respectively, in the maximal value region. Fine mapping of the glioma microcirculation is feasible with dynamic contrast-enhanced synchrotron radiation CT performed with well-controlled analytic protocols. http://radiology.rsnajnls.org/cgi/content/full/2501071929/DC1.

Cryogenic characteristics of sub‐100‐nm‐gate AlGaN/GaN MIS‐HEMTs

AbstractWe measured DC and RF characteristics at 300 and 16 K of sub‐100‐nm‐gate AlGaN/GaN metal‐insulator‐semiconductor (MIS) high electron mobility transistors (HEMTs) that had SiN/SiO2/SiN triple‐layer insulators. The drain‐source current and the maximum transconductance increased as expected. We observed an increase of 14 to 28% in the value of cutoff frequency fT at 16 K over that at 300 K. At 16 K, we obtained a maximum fT of 176 GHz at a gate length Lg of 45 nm. We estimated the average electron velocity under the gate by a transit time analysis. The average velocities were 2.2 × 107 cm/s at 300 K and 2.7 × 107 cm/s at 16 K. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Establishment of reference range for thyroid hormones in normal pregnant Indian women

Interpretation of thyroid function tests during pregnancy needs trimester-related reference intervals from pregnant populations with minimal risk for thyroid dysfunction. While India has become iodine sufficient after two decades of salt iodisation, there is no normative data for thyroid function from healthy pregnant women of this country. To determine trimester-specific reference ranges for free triiodothyronine (FT(3)), free thyroxine (FT(4)) and thyrotropin (TSH) from healthy pregnant Indian women. Cross-sectional study in a reference population of pregnant women. Primary care level obstetric department in India. Women with uncomplicated pregnancy in any trimester. Five hundred and forty-one apparently healthy pregnant women with uncomplicated single intrauterine gestations reporting to the Armed Forces Clinic in any trimester were consecutively recruited. Clinical examination, thyroid ultrasound for echogenicity and nodularity and estimation of FT(3), FT(4), TSH and antithyroid antibodies (antithyroperoxidase [anti-TPO] and antithyroglobulin [anti-Tg]) using electrochemiluminescence technique were carried out. From this entire sample, a disease- and risk-free reference population was obtained by excluding those with any known factor that could affect thyroid function or those who were being treated for thyroid dysfunction. None. Of the 541 consecutive pregnant women in different trimesters enrolled for the study, 210 women were excluded. The composition of reference population comprising 331 women was 107 in first trimester, 137 in second trimester and 87 in third trimester. The 5th and 95th percentiles values were used to determine the reference ranges for FT(3), FT(4) and TSH. The trimester-wise values in the first, second and third trimesters were: FT(3) (1.92-5.86, 3.2-5.73 and 3.3-5.18 pM/l), FT(4) (12-19.45, 9.48-19.58 and 11.32-17.7 pM/l) and TSH (0.6-5.0, 0.44-5.78 and 0.74-5.7 iu/ml), respectively. Analysis of mean, median values for FT(3), FT(4) and TSH between each trimester showed no significant difference in FT(3) and TSH values (95% CI). However, FT(4) showed significant variation between trimesters with values decreasing with advancing gestational age (P value: first versus second = 0.015, first versus third = 0.003 and second versus third = not significant). Women with antibody positivity and hypoechogenicity of thyroid gland had significantly higher TSH values when compared with women with antibody negativity and normoechogenicity. Reference ranges of FT(3), FT(4) and TSH have been established for pregnant Indian women using 5th and 95th percentiles.

Investigation of SOI Substrates Incorporated with Buried MoSi2 for High Frequency SiGe HBTs

Highly arsenic-doped Si-on-insulator (SOI) substrate incorporated with buried MoSi2 layers is fabricated aiming at decreasing the collector series resistance of SiGe heterojunction bipolar transistors (HBTs) on SOI, thereby enhancing cutoff frequency (fT) performance and increasing the maximum value of fT (fTMAX). The fT performance at medium current is enhanced and current required for fT = 15 GHz is reduced by half. The value of fTMAX is improved by 30%.

EMG amplitude and frequency parameters of muscular activity: Effect of resistance training based on electromyographic fatigue threshold

The present study aimed to evaluate the effect of a resistance training program based on the electromyographic fatigue threshold (EMG FT, defined as the highest exercise intensity performed without EMG alterations), on the EMG amplitude (root mean square, RMS) and frequency (median frequency, MF) values for biceps brachii (BB), brachioradialis (BR), triceps brachii (TB) and multifidus (MT). Twenty healthy male subjects, (training group [TG], n = 10; control group [CG], n = 10), firstly performed isometric contractions, and after this, dynamic biceps curl at four different loads to determine the EMG FT. The TG training program used the BB EMG FT value (8 weeks, 2 sessions/week, 3 exhaustive bouts/session, 2 min rest between bouts). No significant differences were found for the isometric force after the training. The linear regression slopes of the RMS with time during the biceps curl presented significant decrease after training for the BB, BR and TB muscles. For the MT muscle, the slope and MF intercept values changed with training. The training program based on the EMG FT influenced EMG the amplitude more than EMG frequency, possibly related to the recruitment patterns of the muscles, although the trunk extensor muscles presented changes in the frequency parameter, showing adaptation to the training program.

Biological markers of liver fibrosis and activity as non-invasive alternatives to liver biopsy in patients with chronic hepatitis C and associated mixed cryoglobulinemia vasculitis

Objective and methods: We assessed the reliability of non-invasive biological scoring indexes (Fibrotest–Actitest [FT–AT], Forns, APRI, age–platelet, platelet, hyaluronic acid) as non-invasive alternatives to liver biopsy (LB) in 138 HCV-infected patients. Results: Thirty-six of 138 (26%) patients had systemic vasculitis, 27% significant serum inflammation, 47% fibrosis (F2F3F4) on LB. The diagnostic value of FT (F2F3F4 vs. F0F1) was assessed by an AUC of 0.83, without difference regarding to systemic vasculitis or serum inflammation. A discordance between FT–AT and the Metavir scoring indexes, present in 29% of patients, was associated with serum hemolysis and male but not with systemic vasculitis or serum inflammation. The other non-invasive biological tests were not influenced by serum inflammation or systemic vasculitis but were less reliable than FT ( P ≤ 0.05). Conclusion: The FT–AT is a reliable non-invasive biochemical alternative to LB in HCV-infected patients with systemic vasculitis and is more reliable than other non-invasive biological indexes.

Biomarkers for the prediction of liver fibrosis in patients with chronic alcoholic liver disease

The aim of this study was to determine the diagnostic use of noninvasive markers of fibrosis in patients with chronic alcoholic liver disease. A total of 221 consecutive patients with an alcohol intake of >50 g/day (median, 100 g/day) and available liver biopsy examination and FibroTest FibroSure (FT) results were included prospectively. Fibrosis was assessed blindly on a 5-stage histologic scale similar to that of the METAVIR scoring system. Hyaluronic acid was measured and used as a standard serum marker of fibrosis. Advanced fibrosis (F2-F4) was present at biopsy examination in 63% of patients. The mean FT value (SE) was F0 = .29 (.05); F1 = .29 (.03), F2 = .40 (.03), F3 = .53 (.04); and F4 = .88 (.02) (P < .05 between all groups, except between F0 and F1). As opposed to FT, there was no significant difference for hyaluronic acid between F2 and F1 and between F2 and F0. For F2-F4 vs. F0-F1, the FT area under the ROC curves (AUROC) = .84 (.03) and .79 (.03) for hyaluronic acid. For the diagnosis of F4, the AUROC was very high, .95 for FT and .93 for hyaluronic acid. The discordances of the 2 stages were attributed to biopsy failures in 26 cases and to FT failures in 13 cases. In heavy drinkers, FT is a simple and noninvasive quantitative estimate of liver fibrosis. The use of FT may decrease the need for liver biopsy examination.

The Nature of Analogue-Based Free Thyroxine Estimates

Clinical laboratories often use analogue-based immunoassays to estimate serum free thyroxine (FT(4)) concentrations. These assays yield FT(4) estimates that correlate closely with thyroxine (T(4)) binding protein concentrations. This correlation implies that either T(4) binding proteins or protein bound T(4) contribute to analogue-based FT(4) values. To study the contributions made by T(4) binding proteins to these FT(4) estimates further, four analogue-based FT(4) assays were applied to: (1) FT(4) solutions without T(4) binding proteins, (2) to T(4) binding protein solutions without T(4), and (3) to total T(4) solutions containing T(4) binding protein, FT(4), and protein-bound T(4). The FT(4) estimates obtained with these solutions ranged from 0.2-8.6 ng/dL, when FT(4) concentrations ranged from less than 0.2-12,000 ng/dL. In the FT(4) solutions, gravimetrically determined FT(4) concentrations were 500-12,000 ng/dL (0.5-12.0 microg/dL) without protein-bound T(4), and the FT(4) estimates obtained were 0.3-6.9 ng/dL. In the total T(4) solutions, dialyzable FT(4) concentrations were less than 0.2-59 ng/dL, retained T(4) concentrations were 499.8-11,441 ng/dL, and the analogue-based FT(4) estimates obtained were 0.2-8.6 ng/dL. Similar FT(4) estimates (0.2-8.6 ng/dL and 0.3-6.9 ng/dL) were obtained with similar concentrations of either protein-bound T(4) or FT(4). Similar test results were associated with similar total T(4) concentrations, not similar FT(4) concentrations. Protein-bound T(4) and T(4) binding protein contributed variably to test results. T(4) quantifications included large analytical losses that are unaccounted for. These assays passed tests of correlation with FT(4) concentrations, but they failed tests of specificity for FT(4) and accuracy in T(4) quantification.

Transient Elevation of Triiodothyronine Caused by Triiodothyronine Autoantibody Associated with Acute Epstein-Barr-Virus Infection

A unique 16-year old female patient presented after acute Epstein-Barr virus (EBV) infection with severe primary hypothyroidism. Her thyroid test results were thyrotropin level (TSH) of 198 mU/L (normal, 0.4-4 mU/L), free thyroxine [FT(4)], 2.5 pmol/L (normal, 10-25 pmol/L), total triiodothyronine (TT(3)) > 19.5 nmol/L (normal, 1.3-2.7 nmol/L), and free triiodothyronine (FT(3)), 0.77 pmol/L (normal, 3.3-6.3 pmol/L). She had high titers of thyroglobulin and thyroid peroxidase autoantibodies. In vitro triiodothyronine (T(3))-binding measured by radioimmunoprecipitation was 86% (normal, up to 8.5%) and thyroxine (T(4))-binding 8.2% (normal, 6.4%). Serum immunoglobulin G (IgG) absorption, achieved by protein-G Sepharose beads, decreased TT(3) toward normal. Levothyroxine treatment normalized the low baseline FT(4) and FT(3) values, and suppressed TSH to normal. However, TT(3) remained highly elevated and returned to normal after 20 months, while T(3 )binding gradually decreased. Thus, her severe hypothyroidism was masked by this unusual phenomenon. Thirty-four patients with EBV infection (15 with acute disease and 19 with previous infection) were tested for thyroid hormone levels. EBV antibodies (early antigen immunoglobulin M [IgM] and IgG and anti-Epstein-Barr virus nuclear antigen [EBNA] IgG) were measured by enzyme-linked immunosorbent assay (ELISA). In 15 patients with acute EBV the mean TT(3) level was 2.47 +/- 0.39 nmol/L (5 had TT(3) values above normal) compared to a mean TT(3) of 1.70 +/- 0.53 nmol/L in 19 subjects with previous infection (p < 0.0005; only 1 had a TT(3) result above normal), with no differences in FT(4) and TSH concentrations between the two groups. Acute EBV infection may be associated with transient mild to severe TT(3) elevation as a result of assay interference by anti-T(3) autoantibodies.

Strain-dependent differences in schedule-induced polydipsia: an assessment in Lewis and Fischer rats

Strain-dependent differences have been used to highlight unknown genetic contributions to important behavioral and physiological end points. In this regard, the Fischer (F344) and Lewis (LEW) rat strains have often been studied because they exhibit a myriad of behavioral and physiological differences. Recently, schedule-induced polydipsia (SIP), a potential model of stress and drug abuse, has been reported to differ between the two strains (see [Pharmacol. Biochem. Behav. 67 (2002) 809]) with F344 rats displaying greater levels of consumption than LEW rats. Given the importance of SIP as a behavioral model of stress and of drug abuse, the present study further explored SIP in F344 and LEW strains by assessing the acquisition and steady-state performance of SIP (under a fixed-time 30 schedule of food delivery; FT30), its characteristic postprandial temporal licking pattern and its modulation by variations in the food delivery schedule (FT15, FT30 and FT60). F344 rats acquired SIP at a faster rate and drank at a higher asymptotic level than LEW rats. Both strains displayed the typical inverted U-shaped post-pellet pattern of drinking and changes in levels of consumption (and displacement of the initiation of post-pellet drinking) with changes in the FT value, supporting the position that the increased drinking seen in both groups was schedule induced. These strain differences in SIP are consistent with the fact that the F344 and LEW strains differ on other behavioral and physiological indices of stress and raise the issue of the use of this model in the assessment of differential drug intake between the two strains.

Testosterone, dehydroepiandrosterone, insulin-like growth factor 1, and insulin in sedentary and physically trained aged men.

The influence of physical activity on dehydroepiandrosterone sulfate (DHEAS), total and free testosterone (TT and FT, respectively), insulin-like growth factor I (IGF-1), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and insulin concentrations in aging men was investigated. Eight trained and nine sedentary men aged 60-65 years volunteered to participate in this study. Physical activity was determined during an effort test and evaluated by the measure of the maximal aerobic power (W(aer,max)). In the trained aging men, the W(aer,max) was higher than in the sedentary group of matching age [mean (SD) 206.8 (17.1) W versus 136.6 (12.3) W; P<0.0001]. The fat percentage was higher in the sedentary (n = 9) than in the trained (n = 8) group [23.9 (3.2)% versus 14.6 (3.7)%; P<0.0001]. DHEAS and IGF-1 levels were higher in trained than in sedentary subjects, respectively 2.04 (1) micromol/l versus 1.01 (0.68) micromol/l (P=0.02) and 192.1 (40.1) ng/ml versus 132.8 (31.2) ng/ml (P= 0.003). Insulin levels were higher in sedentary subjects [11.2 (3.5) mIU/l versus 7.6 (2.2) mIU/l, P=0.03]. No statistical difference was observed between both groups for FT and total TT values, FSH values and LH values. IGF-1 was correlated with W(aer,max) (r = 0.64, P = 0.003), and DHEAS was correlated with IGF-1 (r=0.59, P=0.01). We observed a relationship between fat percentage and each of the following hormones: IGF-1 (r=-0.50, P=0.03), FT (r=-0.66, P= 0.002), TT (r=-0.54, P = 0.02) and insulin (r=0.63, P=0.004). Insulin was inversely correlated with FT (r= -0.66, P=0.002) and TT (r=-0.47, P=0.05). These results suggest that regular physical activity could maintain higher DHEAS and IGF-1 and lean body mass levels in elderly men, and participate in general well being in older age.

Frequency optimization of pseudomorphic modulation-doped field-effect transistor (AlGaAs/InGaAs) for microwave and millimeter-wave applications

The results of an analysis based on the solution of the 2-D Poisson equation are presented to investigate the dependence of the small-signal parameters on biasing conditions. The switching parameters are calculated simply from the charge variations, and it is found that the characteristics depend only on the basic device parameters and terminal voltages. The high value of ft proves the utility of the model in the design of low-power MMICs. A maximum frequency of 101.42 GHz at 0.25 μm is obtained, and the results show close agreement with the experimental data, thereby proving the validity of the proposed model. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 377–383, 2000.

Non-invasive assessment of fluid volume status in theinterstitium after haemodialysis

During dialysis excess fluid is removed from uraemic patients.The excess fluid is mainly located in the skin and subcutaneoustissues. In this study we wished, with two non-invasivetechniques, the IM (impression method) and BIA (bioimpedanceanalysis), to study what mechanical (IM) and electrical cellularmembrane (BIA) effects the fluid withdrawal has on thesetissues. The IM measures the resistive force of the tissues whenmechanically compressed. From the force curve two parametersare calculated, the F(0), indicative of interstitial tissuepressure and the FT corresponding to the translocation of tissuefluid (interstitial movable water).The BIA phase angle shift (ϕ), i.e. geometrical angulartransformation of the ratio between reactance and resistance,which has been associated with cellular membrane function, wasused as a measurement of electrical cellular membrane effects.Twenty patients were studied before and after haemodialysismeasuring the F(0), FT and ϕ. The results showed that thepatients lost a median of 3.7 kg during the haemodialysis. F(0)increased until after dialysis, but did not reach significantvalues, whereas FT increased significantly after dialysis,p < 0.001, as compared with before. After a peak at one hourpostdialysis the FT value returned to predialysis values at fourhours after termination of dialysis. Also ϕ increased frombefore to after dialysis, p < 0.001, but already after one hour itreturned to predialysis values.It is common knowledge that dialysis alters the dynamics of fluidin the interstitium of the skin and subcutis. We conclude that theimpression method is sensitive enough to detect and chroniclethese changes. Furthermore, with the BIA, (phase angle) signs ofchanges in the electrical properties of the tissues, possiblyreflecting cellular membrane function, could be detected.

Performance of AlN/GaN Heterostructure Metal Insulator Semiconductor Field Effect Transistor Based on Two-dimensional Monte Carlo Simulation

We performed a two-dimensional Monte Carlo simulation of an AlN/GaN heterostructure metal insulator semiconductor field effect transistor (hetero-MIS-FET). The vertical structure of the FET is AlN(6 nm)/GaN, and the gate length, the gate-to-source length and the gate-to-drain length are 0.2 µm, 0.2 µm and 0.4 µm, respectively. We assume that GaN and AlN are wurtzite structures and are grown along the c-axis. We took account of the total electric polarization of AlN of 3×10-6 C cm-2 due to piezoelectric and spontaneous polarization. Three valley models for the conduction band of GaN and AlN are employed. The maximum value of the cutoff frequency fT and the transconductance Gm are about 100 GHz (Id=2 A/mm) and 2 S/mm (Vg=0.5 V), respectively. The high fT and Gm values and high Id value when fT is at the maximum strongly suggest that the AlN/GaN hetero-MIS-FET has high potential as a high-frequency, high-power device.