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Following the experimentally observed Seebeck coefficient enhancement in PbTe quantum wells in Pb1−xEuxTe/PbTe multiple-quantum-well structures which indicated the potential usefulness of low dimensionality, we have investigated the thermoelectric properties of PbSexTe1−x/PbTe quantum-dot superlattices for possible improved thermoelectric materials. We have again found enhancements in Seebeck coefficient and thermoelectric figure of merit (ZT) relative to bulk values, which occur through the various physics and materials science phenomena associated with the quantum-dot structures. To date, we have obtained estimated ZT values approximately double the best bulk PbTe values, with estimated ZT as high as about 0.9 at 300 K. [ABSTRACT FROM AUTHOR]

Introduction: Microvolt T wave alternans (TWA) can be arrhythmogenic in patients with cardiomyopathy, particularly when discordant TWA develops from delayed conduction. We hypothesized that QRS fractionation, as a measure of delayed conduction, will improve the accuracy of TWA in predicting ventricular arrhythmias (VA) in patients with hypertrophic cardiomyopathy (HCM).Methods: We prospectively evaluated 97 HCM patients with a preexisting ICD (age 51±15 yrs, 62 male). High resolution (1kHz sampling) 12-lead Holter recordings were made during sinus rhythm and ventricular pacing at 100, 110 and 120 bpm for 3 minutes at each rate. TWA was measured during ventricular pacing using the spectral method that quantifies the maximum alternans magnitude (Valt) and a noise threshold (k). +TWA was defined as Valt >0 µV with k >3. QRS fractionation was measured in each precordial QRS complex during sinus rhythm using custom software that quantifies the number of low amplitude peaks of <25ms duration (QRSp). Ventricular arrhythmia (VA) was assessed as cardiac arrest or appropriate ICD therapy during followup after ICD implant.Results: Over a median follow-up period of 41 (22-98) months, 20% of patients had VA. +TWA was found in 77% of patients. +TWA (21 vs 19%, p=0.54) and Valt (8.4 [2.5-18.6] vs 6.4 [2.5-10.5] µV, p=0.39) were similar between +VA and –VA patients. Sensitivity of +TWA for distinguishing +VA vs –VA was 79%, but specificity and accuracy were poor at 24 and 35%, respectively. QRSp was greater in +VA vs -VA patients (2 [1-3] vs 1[0-2], p=0.024). ROC curve analysis (area under curve 0.66, p=0.03) showed that a QRSp ≥ 2 was the optimal cutpoint for distinguishing +VA vs –VA (sensitivity 58%, specificity 65%, accuracy 64%). The proportion of patients with both QRSp ≥ 2 and +TWA was 31%. QRSp ≥2 and +TWA together achieved higher specificity (74%) and accuracy (70%) with similar sensitivity (53%) when compared to QRSp ≥ 2 alone. Patients with both QRSp ≥ 2 and +TWA had greater VA events compared to those without (33 vs 13%, p=0.03).Conclusions: In HCM, the presence of both QRS fractionation and +TWA identifies patients at risk of VA more accurately than either measure alone. The conduction delay causing QRS fractionation may promote more arrhythmogenic discordant TWA; thereby increasing arrhythmia vulnerability. [ABSTRACT FROM PUBLISHER]