We discuss the physical origin and effects of micrononuniformities on thin-film photovoltaics. The key factors are the large device area and the presence of potential barriers in the grain boundaries (for polycrystalline films) and in device junctions. We model the nonuniformity effects in the terms of random microdiodes connected in parallel through a resistive electrode. The microdiodes of low open circuit voltages are shown to affect macroscopically large regions. They strongly reduce the device performance and induce its nonuniform degradation in several different modes. We support our predictions by experiments, which show that the device degradation is driven by the light-induced forward bias and is spatially nonuniform.
Summary Substance P (SP) is a neuropeptide with neuroimmunoregulatory activity that may play a role in susceptibility to infection. Human mast cells, which are important in innate immune responses, were analysed for their responses to pathogen‐associated molecules via Toll‐like receptors (TLRs) in the presence of SP. Human cultured mast cells (LAD2) were activated by SP and TLR ligands including lipopolysaccharide (LPS), Pam3CysSerLys4 (Pam3CSK4) and lipoteichoic acid (LTA), and mast cell leukotriene and chemokine production was assessed by enzyme‐linked immunosorbent assay (ELISA) and gene expression by quantitative PCR (qPCR). Mast cell degranulation was determined using a β‐hexosaminidase (β‐hex) assay. SP treatment of LAD2 up‐regulated mRNA for TLR2, TLR4, TLR8 and TLR9 while anti‐immunoglobulin E (IgE) stimulation up‐regulated expression of TLR4 only. Flow cytometry and western blot confirmed up‐regulation of TLR2 and TLR8. Pretreatment of LAD2 with SP followed by stimulation with Pam3CSK4 or LTA increased production of leukotriene C4 (LTC4) and interleukin (IL)‐8 compared with treatment with Pam3CSK4 or LTA alone (> 2‐fold; P < 0·01). SP alone activated 5‐lipoxygenase (5‐LO) nuclear translocation but also augmented Pam3CSK4 and LTA‐mediated 5‐LO translocation. Pam3CSK4, LPS and LTA did not induce LAD2 degranulation. SP primed LTA and Pam3CSK4‐mediated activation of JNK, p38 and extracellular‐signal‐regulated kinase (ERK) and activated the nuclear translocation of c‐Jun, nuclear factor (NF)‐κB, activating transcription factor 2 (ATF‐2) and cyclic‐AMP‐responsive element binding protein (CREB) transcription factors. Pretreatment with SP followed by LTA stimulation synergistically induced production of chemokine (C‐X‐C motif) ligand 8 (CXCL8)/IL‐8, chemokine (C‐C motif) ligand 2 (CCL2)/monocyte chemotactic protein 1 (MCP‐1), tumour necrosis factor (TNF) and IL‐6 protein. SP primes TLR2‐mediated activation of human mast cells by up‐regulating TLR expression and potentiating signalling pathways associated with TLR. These results suggest that neuronal responses may influence innate host defence responses.
The double-well potential model, well known to describe many low-temperature properties of amorphous materials, has been extended to incorporate effects of high pressures. The resulting model not only explains the temperature and time dependences of pressure-induced phenomena but also provides possible explanations for thermal annealing effects as well as irradiation compaction. The results of Brillouin-light-scattering experiments designed to test various predictions of the model are presented: good agreement is obtained.
The equilibrium ON and OFF states of resistive random access memory (RRAM) are due to formation and destruction of a conducting filament. The laws of thermodynamics dictate that these states correspond to the minimum of free energy. Here, we develop a numerical model that, through the minimization of free energy at a given voltage, determines the filament parameters and thus the electric current. Overall, it simulates the current-voltage (I-V) characteristics of RRAM. The model describes mutual transformations of RRAM states through SET (ON→OFF) and RESET (OFF→ON) processes. From the modeling perspectives, these states and processes constitute four programming modules constructed here in COMSOL Multiphysics software tackling the electrodynamic and heat transfer equations and yielding RRAM energy and I-V. Our modeling uniquely reproduces the observed I-V varying with voltage ramp-rates. That is achieved by accounting for the ramp-rate dependent activation energy of conduction. The underlying mechanism is due to the deformation interaction caused by the double well atomic potentials universally present in amorphous materials and having exponentially broad distribution of relaxation times. As another unique feature, our modeling reproduces the observed cycle-to-cycle variations of RRAM parameters attributed to the lack of self-averaging in small ensembles of double well potentials and electronic states in geometrically small (nano-size) RRAM structures. * Electronic address: dipesh.niraula@rockets.utodeo.edu † Electronic address: victor.karpov@utoledo.edu FIG. 1: Top left: Schematic of the circuitry where input voltage source VS, load resistor RL and a simple RRAM device RD are connected in series. Bottom left: plot of input voltage pulse where λ is the voltage ramp-rate and Vamp is the amplitude. Top right: Representation of a typical I-V characteristics of RRAM [4-7]. VD is the voltage drop across RRAM device. The SET current ISET is the maximum current limited by the Vamp. Bottom right: Customary representation of the I-V with absolute valued current axis. The dashed domain represents very fast nucleation processes.the source voltage ramping; they represent the SET and RESET processes. Their characteristic features are voltage snapback A-B followed by the vertical domain B-C for SET, and voltage snapforward D-E followed by the horizontal domain E-F for RESET. arXiv:1806.01397v2 [cond-mat.mes-hall]
Our analysis of the experimental data related to nonphotochemical laser induced nucleation in solutions leads to the inevitable conclusion that the phase transformation is initiated by particles that are metallic in nature. This conclusion appears paradoxical because the final products are dielectric crystals. We show that the experimental results are well accounted for by the theory of electric field induced nucleation of metallic particles that are elongated in the direction of the field. However, new physical and chemical insights are required to understand the structure of the metallic precursor particles and the kinetics of subsequent dielectric crystallization.PACS numbers: 05.70. Fh, 64.60.qj, 64.70.dg, 82.60.Nh There is growing experimental support for electric field induced nucleation of solute particles in supersaturated solutions. First reported by Garetz et. al. [1], the phenomenon referred to as nonphotochemical laser induced nucleation (NPLIN) has been observed with both oscillating [1][2][3][4][5][6][7] and static [8] fields. The term 'nonphotochemical' emphasizes that there is no light absorption; hence, underlying changes in electronic structure capable of chemical reactions are ruled out. In all of the above cases, the final product of nucleation was found to be small dielectric particles.A clear indication that the field is the primary phase change driver is the alignment of nucleated particles along the direction of the applied field (or laser beam polarization). That phenomenon has led to a type of 'polarization switching' wherein the polymorph (crystal structure) of the nucleated crystal can be controlled by applying either linear or circular polarized light [2,3]. The underlying mechanism remains an open question with many practical implications [9].Our summary of NPLIN data from the literature is presented in Fig. 1 where the peak laser intensity (or applied field) and exposure time are provided at which crystallization was eventually observed in solutions at various supersaturation levels. For our purposes, the most important results are that: i) the field reduces the nucleation time by 13 orders of magnitude or even larger; and ii) it can do so at optical frequencies (∼ 10 14 Hz). Other observations include the existence of a threshold field, below which nucleation did not occur, and a linear type correlation between the cumulative fraction of samples nucleated and laser intensity [2,6], as well as the solute supersaturation [6].The anomalous strength of the observed field effect can be conveniently expressed in the terms of nucleation barrier W 0 that determines the nucleus induction time, τ = τ 0 exp (W 0 /kT ). Here, τ 0 > ∼ 10 −13 s is the characteristic atomic vibration or diffusion time, k is Boltzmann's constant, and T is temperature. The observed reduction of τ by a factor of 10 −13 requires decreasing the nucleation barrier by approximately ∆W (E) = W 0 −W (E) ∼ 30kT . The ordinate is the peak applied field (unless labeled as the threshold field) at which nucleation occurred...
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