On the dimension of Voisin sets in the moduli space of abelian varieties

We study the subsets $V_k(A)$ of a complex abelian variety $A$ consisting in the collection of points $x\in A$ such that the zero-cycle $\{x\}-\{0_A\}$ is $k$-nilpotent with respect to the Pontryagin product in the Chow group. These sets were introduced recently by Voisin and she showed that $\dim V_k(A) \leq k-1$ and $V_k(A)$ is countable for a very general abelian variety of dimension at least $2k-1$. We study in particular the locus $\mathcal V_{g,2}$ in the moduli space of abelian varieties of dimension $g$ with a fixed polarization, where $V_2(A)$ is positive dimensional. We prove that an irreducible subvariety $\mathcal Y \subset \mathcal V_{g,2}$, $g\ge 3$, such that for a very general $y \in \mathcal Y$ there is a curve in $V_2(A_y)$ generating $A$ satisfies $\dim \mathcal Y \le 2g - 1.$ The hyperelliptic locus shows that this bound is sharp.Comment: Final version to appear in Mathematische Annale

L’inibizione tireotropinica da metformina non si associa a segni cardiologici di ipertiroidismo subclinico

Recenti dati di letteratura hanno evidenziato come metformina determini una riduzione/soppressione dei livelli sierici di tireotro- pina (TSH), simulando un ipertiroidismo subclinico il cui signifi- cato clinico rimane a oggi ancora assai controverso. Sebbene l’ipertiroidismo subclinico sia nella maggioranza dei casi una condizione clinica asintomatica, è altrettanto noto come esso si associ a un aumentato rischio di aritmie (più frequentemente la fibrillazione atriale) e ad alterazioni morfo-funzionali cardiache determinando un aumento di morbilità e mortalità cardiovasco- lare. Scopo del presente studio è stato quello di valutare retrospetti- vamente le alterazioni di differenti indici elettrocardiografici in pazienti diabetici eutiroidei che, dopo aver intrapreso terapia con metformina, hanno sviluppato riduzione/soppressione dei valori di TSH comparando i dati con quelli ottenuti in pazienti con iper- tiroidismo subclinico secondario a patologie tiroidee o a terapia soppressiva con L-tiroxina. I parametri elettrocardiografici (frequenza cardiaca, durata del- l’onda P, indice di dispersione dell’onda P, QT max, QT min, indice di dispersione dell’intervallo QT) sono stati valutati in 23 pazienti diabetici in terapia con metformina prima e dopo 6 mesi dall’instaurarsi della soppressione del TSH e in 31 con- trolli con ipertiroidismo subclinico. Nessuna modifica significa- tiva è stata osservata tra i parametri elettrocardiografici rilevati prima e dopo la riduzione del TSH. Al contrario, significative dif- ferenze nella durata dell’onda P (102,9 ± 7,4 vs 92,1 ± 5,8 ms, p < 0,001), dell’indice di dispersione dell’onda P (13,1 ± 3,4 vs 7,1 ± 3,5 ms, p < 0,001), del QT max (399 ± 18 vs 388 ± 16 ms, p = 0,024), del QT min (341 ± 14 vs 350 ± 17 ms, p = 0,038) e di quello dell’intervallo QT (49,9 ± 9,6 vs 30,9 ± 9,2 ms, p < 0,001) sono state rilevate tra i controlli con iperti- roidismo subclinico e il gruppo di pazienti diabetici con valori ridotti/soppressi di TSH. I risultati del nostro studio evidenzierebbero come l’effetto di riduzione/soppressione del TSH osservato in alcuni pazienti dia- betici in terapia con metformina non si associ a marker periferi- ci cardiaci da eccesso di ormoni tiroidei. L’alterazione del profilo tiroideo metformina-indotto sembrerebbe non indicativo di iper- tiroidismo subclinico, suggerendo quindi che non sussiste la necessità di sottoporre a stretti controlli della funzione tiroidea i pazienti diabetici in terapia con metformin

On the dimension of Voisin sets in the moduli space of abelian varieties

We study the subsets $V_k(A)$ of a complex abelian variety $A$ consisting in the collection of points $x \in A$ such that the zero-cycle $\{x\}-\left\{0_A\right\}$ is $k$-nilpotent with respect to the Pontryagin product in the Chow group. These sets were introduced recently by Voisin and she showed that $\operatorname{dim} V_k(A) \leq k-1$ and $\operatorname{dim} V_k(A)$ is countable for a very general abelian variety of dimension at least $2 k-1$. We study in particular the locus $\mathcal{V}_{g, 2}$ in the moduli space of abelian varieties of dimension $g$ with a fixed polarization, where $V_2(A)$ is positive dimensional. We prove that an irreducible subvariety $\mathcal{Y} \subset \mathcal{V}_{g, 2}$, $g \geq 3$, such that for a very general $y \in \mathcal{Y}$ there is a curve in $V_2\left(A_y\right)$ generating $A$ satisfies $\operatorname{dim} \mathcal{Y} \leq 2 g-1$. The hyperelliptic locus shows that this bound is sharp

An overview on recent developments in RF and microwave power H-terminated diamond MESFET technology

Thanks to its wide bandgap, exceptionally high thermal conductivity and relatively high carrier velocities, diamond exhibits attractive semiconductor properties that make it an interesting candidate for high power, high frequency and high temperature solid-state microelectronic devices, able to withstand harsh environmental conditions (in terms of temperature and/or radiation). The development of a diamond transistor technology has been restricted for many years due to the difficulty in implementing conventional acceptor or donor bulk doping strategies with satisfactory activation at room temperature. More recently, a breakthrough in diamond MESFET technology was represented by the introduction of surface diamond p-doping by means of H-termination, opening the way to interesting development in the microwave field. The paper presents an overview on recent developments in H-terminated diamond MESFETs for power RF and microwave applications. After an introduction to the diamond technology and device state-of-the-art performance, the physics-based and large-signal modeling of diamond MESFETs is discusse

A Case of Concurrent Riedel's, Hashimoto's and Acute Suppurative Thyroiditis

Riedel's thyroiditis (RT) is a rare form of infiltrative and inflammatory disease of the thyroid, first described by Bernard Riedel in 1896. The concurrent presence of RT and other thyroid diseases has been reported, but, the association of RT with Hashimoto's thyroiditis and acute thyroiditis has not yet been reported. We present a case of concurrent Riedel's, Hashimoto's and acute thyroiditis that occurred in a 45-year-old patient

Ka-band 4 W GaN/Si MMIC power amplifier for CW radar applications

In this contribution it is reported the design, implementation and characterization of a 4-stage single-ended Ka-band power amplifier based on 100 nm GaN/Si commercial process. The amplifier, designed for CW radar applications, has been measured under small-signal and pulsed large-signal conditions. The amplifier exhibits an output power above 4W, together with power added efficiency in excess of 28 % and operative gain larger than 25dB over the 34GHz-38GHz frequency range

Analysis of turbulence effects in a patient-specific aorta with aortic valve stenosis

Blood flow in the aorta is often assumed laminar, however aortic valve pathologies may induce transition to turbulence and our understanding of turbulence effects is incomplete. The aim of the study was to provide a detailed analysis of turbulence effects in aortic valve stenosis (AVS). Methods: Large-eddy simulation (LES) of flow through a patient-specific aorta with AVS was conducted. Magnetic resonance imaging (MRI) was performed and used for geometric reconstruction and patient-specific boundary conditions. Computed velocity field was compared with 4D flow MRI to check qualitative and quantitative consistency. The effect of turbulence was evaluated in terms of fluctuating kinetic energy, turbulence-related wall shear stress (WSS) and energy loss. Results: Our analysis suggested that turbulence was induced by a combination of a high velocity jet impinging on the arterial wall and a dilated ascending aorta which provided sufficient space for turbulence to develop. Turbulent WSS contributed to 40% of the total WSS in the ascending aorta and 38% in the entire aorta. Viscous and turbulent irreversible energy losses accounted for 3.9 and 2.7% of the total stroke work, respectively. Conclusions: This study demonstrates the importance of turbulence in assessing aortic haemodynamics in a patient with AVS. Neglecting the turbulent contribution to WSS could potentially result in a significant underestimation of the total WSS. Further work is warranted to extend the analysis to more AVS cases and patients with other aortic valve diseases

Evaluation of computational methodologies for accurate prediction of wall shear stress and turbulence parameters in a patient-specific aorta

Background: Recent studies suggest that blood flow in main arteries is intrinsically disturbed, even under healthy conditions. Despite this, many computational fluid dynamics (CFD) analyses of aortic haemodynamics make the assumption of laminar flow, and best practices surrounding appropriate modelling choices are lacking. This study aims to address this gap by evaluating different modelling and post-processing approaches in simulations of a patient-specific aorta. Methods: Magnetic resonance imaging (MRI) and 4D flow MRI from a patient with aortic valve stenosis were used to reconstruct the aortic geometry and derive patient-specific inlet and outlet boundary conditions. Three different computational approaches were considered based on assumed laminar or assumed disturbed flow states including low-resolution laminar (LR-laminar), high-resolution laminar (HR-Laminar) and large-eddy simulation (LES). Each simulation was ran for 30 cardiac cycles and post-processing was conducted on either the final cardiac cycle, or using a phase-averaged approach which utilised all 30 simulated cycles. Model capabilities were evaluated in terms of mean and turbulence-based parameters. Results: All simulation types, regardless of post-processing approach could correctly predict velocity values and flow patterns throughout the aorta. Lower resolution simulations could not accurately predict gradient-derived parameters including wall shear stress and viscous energy loss (largest differences up to 44.6% and 130.3%, respectively), although phase-averaging these parameters improved predictions. The HR-Laminar simulation produced more comparable results to LES with largest differences in wall shear stress and viscous energy loss parameters up to 5.1% and 11.6%, respectively. Laminar-based parameters were better estimated than turbulence-based parameters. Conclusions: Our findings suggest that well-resolved laminar simulations can accurately predict many laminar-based parameters in disturbed flows, but there is no clear benefit to running a HR-Laminar simulation over an LES simulation based on their comparable computational cost. Additionally, post-processing ‘typical’ laminar simulation results with a phase-averaged approach is a simple and cost-effective way to improve accuracy of lower-resolution simulation results