328 research outputs found
Transient Non-linear Thermal FEM Simulation of Smart Power Switches and Verification by Measurements
Thermal FEM (Finite Element Method) simulations can be used to predict the
thermal behavior of power semiconductors in application. Most power
semiconductors are made of silicon. Silicon thermal material properties are
significantly temperature dependent. In this paper, validity of a common
non-linear silicon material model is verified by transient non-linear thermal
FEM simulations of Smart Power Switches and measurements. For verification,
over-temperature protection behavior of Smart Power Switches is employed. This
protection turns off the switch at a pre-defined temperature which is used as a
temperature reference in the investigation. Power dissipation generated during
a thermal overload event of two Smart Power devices is measured and used as an
input stimulus to transient thermal FEM simulations. The duration time of the
event together with the temperature reference is confronted with simulation
results and thus the validity of the silicon model is proved. In addition, the
impact of non-linear thermal properties of silicon on the thermal impedance of
power semiconductors is shown.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Pukotine na kalupima (alatima) za tlačno lijevanje uslijed toplinskog umora
Die-casting dies are exposed to high thermal and mechanical loads. Thermal fatigue cracking of dies due to thermal cycling may importantly shorten the life-time of the die. Cracks degrade the surface quality of dies and consequently the surface of castings. In this study, thermal fatigue cracking of dies was analyzed during the process of die casting aluminium alloys. During the process cracks were observed and measured and their location and size were determined. Thermal and mechanical loads cause high local stresses and consequently surface cracks. First cracks occur as early as after 2000 cycles and propagate progressively with cycles.Kalupi (alati) za lijevanje pod tlakom su izloženi velikim toplinskim i mehaničkim opterećenjima. Pukotine uslijed toplinskog umora su zbog izmjene toplinskih ciklusa važan ograničavajući mehanizam životnoga vijeka kalupa. Pukotine smanjuju (degradiraju) kvalitetu površine kalupa i posljedično površinu odljevka. U ovom radu su analizirane pukotine nastale na kalupu zbog toplinskog umora tokom tlačnog lijevanja aluminija. Tokom procesa su promatranjem i mjerenjem utvrđene lokacije i veličine nastalih pukotina na kalupu. Toplinska i mehanička opterećenja uzrokuju velika lokalna naprezanja i posljedično pukotine na površini kalupa. Prva pukotina pojavljuje se već nakon 2000 ciklusa i progresivno se širi povećanjem broja ciklusa
Stability of the Shallow Axisymmetric Parabolic-Conic Bimetallic Shell by Nonlinear Theory
In this contribution, we discuss the stress, deformation, and snap-through conditions of thin, axi-symmetric, shallow bimetallic shells of so-called parabolic-conic and plate-parabolic type shells loaded by thermal loading. According to the theory of the third order that takes into account the balance of forces on a deformed body, we present a model with a mathematical description of the system geometry, displacements, stress, and thermoelastic deformations. The equations are based on the large displacements theory. We numerically calculate the deformation curve and the snap-through temperature using the fourth-order Runge-Kutta method and a nonlinear shooting method. We show how the temperature of both snap-through depends on the point where one type of the rotational curve transforms into another
Wnt/β-catenin signalling induces MLL to create epigenetic changes in salivary gland tumours
We show that activation of Wnt/{beta}-catenin and attenuation of Bmp signals, by combined gain- and loss-of-function mutations of {beta}-catenin and Bmpr1a, respectively, results in rapidly growing, aggressive squamous cell carcinomas (SCC) in the salivary glands of mice. Tumours contain transplantable and hyperproliferative tumour propagating cells, which can be enriched by fluorescence activated cell sorting (FACS). Single mutations stimulate stem cells, but tumours are not formed. We show that {beta}-catenin, CBP and Mll promote self-renewal and H3K4 tri-methylation in tumour propagating cells. Blocking {beta}-catenin-CBP interaction with the small molecule ICG-001 and small-interfering RNAs against {beta}-catenin, CBP or Mll abrogate hyperproliferation and H3K4 tri-methylation, and induce differentiation of cultured tumour propagating cells into acini-like structures. ICG-001 decreases H3K4me3 at promoters of stem cell-associated genes in vitro and reduces tumour growth in vivo. Remarkably, high Wnt/{beta}-catenin and low Bmp signalling also characterize human salivary gland SCC and head and neck SCC in general. Our work defines mechanisms by which {beta}-catenin signals remodel chromatin and control induction and maintenance of tumour propagating cells. Further, it supports new strategies for the therapy of solid tumours
Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires
The future developments of three-dimensional magnetic nanotechnology require
the control of domain wall dynamics by means of current pulses. While this has
been extensively studied in planar magnetic strips (planar nanowires), few
reports exist in cylindrical geometry, where Bloch point domain walls are
expected to have intriguing properties. Here we report this investigation in
cylindrical magnetic Ni nanowires with geometrical notches. Experimental work
based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with
photoemission electron microscopy (PEEM) indicates that large current densities
induce domain wall nucleation while smaller currents move domain walls
preferably against the current direction. In the region where no pinning
centers are present we found domain wall velocity of about 1 km/s. The domain
wall motion along current was also detected in the vicinity of the notch
region. Pinning of domain walls has been observed not only at geometrical
constrictions but also outside of them. Thermal modelling indicates that large
current densities temporarily raise the temperature in the nanowire above the
Curie temperature leading to nucleation of domain walls during the system
cooling. Micromagnetic modelling with spin-torque effect shows that for
intermediate current densities Bloch point domain walls with chirality parallel
to the Oersted field propagate antiparallel to the current direction. In other
cases, domain walls can be bounced from the notches and/or get pinned outside
their positions. We thus find that current is not only responsible for the
domain wall propagation but is also a source of pinning due to the Oersted
field action
Cognitive Functioning in Patients Remitted from Recurrent Depression: Comparison with Acutely Depressed Patients and Controls and Follow-up of a Mindfulness-Based Cognitive Therapy Trial
Mindfulness-Based Cognitive Therapy (MBCT) is a promising intervention to prevent depressive relapse. Yet beyond efficacy studies, little is known regarding the mechanisms that could be modified through MBCT. Objectives of the present study were twofold: determine whether cognitive functioning was altered among patients remitted from depression at admission in a MBCT trial; and document possible changes during the trial and follow-up. In a cross-sectional perspective, cognitive functioning (autobiographical memory, shifting capacities, dysfunctional attitudes, mindful attention awareness and rumination habits) was first compared between 36 patients remitted from depression, 20 acutely depressed patients and 20 control participants. In a longitudinal perspective, changes in the remitted sample were explored during a MBCT plus Treatment As Usual versus Treatment As Usual randomized controlled trial and 9-month follow-up. Performances of remitted patients were similar to the ones of control participants for autobiographical memories, shifting capacities, and mindful attention awareness, whereas levels of rumination and dysfunctional attitudes were significantly elevated. Participation in the MBCT program was accompanied with a significant decrease of dysfunctional attitudes that continued up to 9-month postintervention. No other change was observed that was specific to MBCT. Results suggest that MBCT might help people to identify dysfunctional attitudes at a very early stage and to avoid engaging further in these attitude
Epigenetic modifier balances Mapk and Wnt signalling in differentiation of goblet and Paneth cells
Differentiation and lineage specification are controlled by cooperation of growth factor signalling. The involvement of epigenetic regulators in lineage specification remains largely elusive. Here, we show that the histone methyltransferase Mll1 prevents intestinal progenitor cells from differentiation, whereas it is also involved in secretory lineage specification of Paneth and goblet cells. Using conditional mutagenesis in mice and intestinal organoids, we demonstrate that loss of Mll1 renders intestinal progenitor cells permissive for Wnt-driven secretory differentiation. However, Mll1-deficient crypt cells fail to segregate Paneth and goblet cell fates. Mll1 deficiency causes Paneth cell-determined crypt progenitors to exhibit goblet cell features by unleashing Mapk signalling, resulting in increased numbers of mixed Paneth/goblet cells. We show that loss of Mll1 abolishes the pro-proliferative effect of Mapk signalling in intestinal progenitor cells and promotes Mapk-induced goblet cell differentiation. Our data uncover Mll1 and its downstream targets Gata4/6 as a regulatory hub of Wnt and Mapk signalling in the control of lineage specification of intestinal secretory Paneth and goblet cells
Bioinspired Ciliary Force Sensor for Robotic Platforms
© 2017 IEEE. The detection of small forces is of great interest in any robotic application that involves interaction with the environment (e.g., objects manipulation, physical human-robot interaction, minimally invasive surgery), since it allows the robot to detect the contacts early on and to act accordingly. In this letter, we present a sensor design inspired by the ciliary structure frequently found in nature, consisting of an array of permanently magnetized cylinders (cilia) patterned over a giant magnetoresistance sensor (GMR). When these cylinders are deformed in shape due to applied forces, the stray magnetic field variation will change the GMR sensor resistivity, thus enabling the electrical measurement of the applied force. In this letter, we present two 3 mm × 3 mm prototypes composed of an array of five cilia with 1 mm of height and 120 and 200 μm of diameter for each prototype. A minimum force of 333 μ N was measured. A simulation model for determining the magnetized cylinders average stray magnetic field is also presented
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