Tumor Growth Rate Approximation-Assisted Estimation

From tumor to tumor, there is a great variation in the proportion of cancer cells growing and making daughter cells that ultimately metastasize. The differential growth within a single tumor, however, has not been studied extensively and this may be helpful in predicting the aggressiveness of a particular cancer type. The estimation problem of tumor growth rates from several populations is studied. The baseline growth rate estimator is based on a family of interacting particle system models which generalize the linear birth process as models of tumor growth. These interacting models incorporate the spatial structure of the tumor in such a way that growth slows down in a crowded system. Approximation-assisted estimation strategy is proposed when initial values of rates are known from the previous study. Some alternative estimators are suggested and the relative dominance picture of the proposed estimator to the benchmark estimator is investigated. An over-riding theme of this article is that the suggested estimation method extends its traditional counterpart to non-normal populations and to more realistic cases

Zigzag graphene nanoribbons without inversion symmetry

Graphene on a substrate will suffer an inversion-symmetry-breaking (ISB) lattice potential. Taking electron-electron interaction into account, we study in this paper the possibility of half-metallicity and noncollinear (NC) magnetic phase for graphene zigzag nanoribbons without inversion symmetry. At half-filling it is found that half-metallic(HM) state can be achieved at an intermediate value of the ISB potential due to its competition with the electron-electron interaction. Away from half-filling, the phase diagrams of doping versus ISB potential for different ribbon width are given, where the regimes for the HM states and NC magnetic state are clearly indicated and discussed. For ribbons with perfect edges, we predict a topological transition between two HM states with different magnetic structures, which is accompanied by an abrupt transition of electrical conductance along the ribbon from $2e^2/h$ to $e^2/h$.Comment: 7 pages, 7 figure

Anomalous impact of thermal fluctuations on spintransfer torque induced ferrimagnetic switching

The dynamics of a spin torque driven ferrimagnetic (FiM) system is investigated using the two-sublattice macrospin model. We demonstrate an ultrafast switching in the picosecond range. However, we find that the excessive current leads to the magnetic oscillation. Therefore, faster switching cannot be achieved by unlimitedly increasing the current. By systematically studying the impact of thermal fluctuations, we find the dynamics of FiMs can also be distinguished into the precessional region, the thermally activated region, and the cross-over region. However, in the precessional region, there is a significant deviation between FiM and ferromagnet (FM), i.e., the FM is insensitive to thermal fluctuations since its switching is only determined by the amount of net charge. In contrast, we find that the thermal effect is pronounced even a very short current pulse is applied to the FiM. We attribute this anomalous effect to the complex relation between the anisotropy and overdrive current. By controlling the magnetic anisotropy, we demonstrate that the FiM can also be configured to be insensitive to thermal fluctuations. This controllable thermal property makes the FiM promising in many emerging applications such as the implementation of tunable activation functions in the neuromorphic computing.Comment: 27 pages, 8 figure

Effects of Wettability and Minerals on Residual Oil Distributions Based on Digital Rock and Machine Learning

AbstractThe wettability of mineral surfaces has significant impacts on transport mechanisms of two-phase flow, distribution characteristics of fluids, and the formation mechanisms of residual oil during water flooding. However, few studies have investigated such effects of mineral type and its surface wettability on rock properties in the literature. To unravel the dependence of hydrodynamics on wettability and minerals distribution, we designed a new experimental procedure that combined the multiphase flow experiments with a CT scan and QEMSCAN to obtain 3D digital models with multiple minerals and fluids. With the aid of QEMSCAN, six mineral components and two fluids in sandstones were segmented from the CT data based on the histogram threshold and watershed methods. Then, a mineral surface analysis algorithm was proposed to extract the mineral surface and classify its mineral categories. The in situ contact angle and pore occupancy were calculated to reveal the wettability variation of mineral surface and distribution characteristics of fluids. According to the shape features of the oil phase, the self-organizing map (SOM) method, one of the machine learning methods, was used to classify the residual oil into five types, namely, network, cluster, film, isolated, and droplet oil. The results indicate that each mineral’s contribution to the mineral surface is not proportional to its relative content. Feldspar, quartz, and clay are the main minerals in the studied sandstones and play a controlling role in the wettability variation. Different wettability samples show various characteristics of pore occupancy. The water flooding front of the weakly water-wet to intermediate-wet sample is uniform, and oil is effectively displaced in all pores with a long oil production period. The water-wet sample demonstrates severe fingering, with a high pore occupancy change rate in large pores and a short oil production period. The residual oil patterns gradually evolve from networks to clusters, isolated, and films due to the effects of snap-off and wettability inversion. This paper reveals the effects of wettability of mineral surface on the distribution characteristics and formation mechanisms of residual oil, which offers us an in-deep understanding of the impacts of wettability and minerals on multiphase flow and helps us make good schemes to improve oil recovery

Effects of 1.84 GHz radio-frequency electromagnetic field on sperm maturation in epididymis microenvironment

In recent years, intense interest has been drawn to the effects of radio-frequency electromagnetic field (RF-EMF) on reproduction. To explore the effects of RF-EMF on sperm maturation in epididymis microenvironment, 24 male Sprague Dawley (SD) rats were randomly divided into three exposed groups (SAR 1, 2 and 4 W/kg) and one sham group. The rats in exposed group were exposed to 1.84 GHz RFEMF for 5 days (1 h/day). After that, the rats were anaesthetized immediately and epididymis were taken out. Half of them were fixed in 4% formalin and the others were placed in tissue homogenate. The morphology of sperm and microstructure of epididymis were observed under microscope after hematoxylin eosin (HE) staining. Expression of Bin1b protein was detected by immunohistochemistry; the level of glutathione (GSH) and enzymes including superoxide dismutase (SOD), acid  phosphatase (ACP), alkaline phosphatase (ALP) and disaccharidase were determined by commercial kits. It was found that,  compared with sham group, the sperm morphology and microstructure of epididymis did not change obviously; similarly, there was no significant change in Bin1b protein expression and the levels of GSH, SOD, ACP and ALP in exposure group. These results  suggest that 1.84 GHz RF-EMF under this experimental condition could not affect the sperm maturation in epididymis  microenvironment of SD rats.Keywords: 1.84 GHz, radio-frequency electromagnetic field (RF-EMF), epididymis, sperm maturation, Bin1

Restoration of NBD1 Thermal Stability Is Necessary and Sufficient to Correct ∆F508 CFTR Folding and Assembly

CFTR (ABCC7), unique among ABC exporters as an ion channel, regulates ion and fluid transport in epithelial tissues. Loss of function due to mutations in the cftr gene causes cystic fibrosis (CF). The most common CF-causing mutation, the deletion of F508 (ΔF508) from the first nucleotide binding domain (NBD1) of CFTR, results in misfolding of the protein and clearance by cellular quality control systems. The ΔF508 mutation has two major impacts on CFTR: reduced thermal stability of NBD1 and disruption of its interface with membrane-spanning domains (MSDs). It is unknown if these two defects are independent and need to be targeted separately. To address this question we varied the extent of stabilization of NBD1 using different second site mutations and NBD1 binding small molecules with or without NBD1/MSD interface mutation. Combinations of different NBD1 changes had additive corrective effects on ΔF508 maturation that correlated with their ability to increase NBD1 thermostability. These effects were much larger than those caused by interface modification alone and accounted for most of the correction achieved by modifying both the domain and the interface. Thus, NBD1 stabilization plays a dominant role in overcoming the ΔF508 defect. Furthermore, the dual target approach resulted in a locked-open ion channel that was constitutively active in the absence of the normally obligatory dependence on phosphorylation by protein kinase A. Thus, simultaneous targeting of both the domain and the interface, as well as being non-essential for correction of biogenesis, may disrupt normal regulation of channel function