Appearance Of Protrusions Research Articles

Change in the Morphology of the Surface of Ta–W Coating after Exposure to Cyclic Laser Pulses

The effect of low-energy pulsed laser irradiation (laser LRS-150A, λ = 1.06 μm) on the surface of Ta–10% W coating produced by ion-plasma deposition in vacuum was investigated. The coating thickness was ~250 μm. With the help of the metallography method, it was shown that the coating average grain size was ~25 μm. The laser pulse energy was 30 J, pulse duration τ = 14 × 10–3 s, and the interval between laser pulses was 7.5 s. The laser beam was focused on the sample surface into a spot with a diameter of 5 mm. The microrelief of the coating surface was investigated with the use of a TESCAN VEGA II scanning electron microscope. X-ray microanalysis in the scanning line of the surface and cross section of the coating and the substrate was carried out on an INCA Energy 250 energy dispersive spectrometer. It was shown that, after a multicycle laser irradiation (200 pulses), numerous rounded protrusions appeared on the surface of the coating. The diameter of the protrusions ranged from 25 to 225 μm and their maximum height was 30 μm. In the irradiation zone, redistribution of W occurred. The concentration of W in the region of the protrusions decreased substantially and increased in the ranges between the protrusions. It was concluded that the appearance of protrusions on the surface of irradiated surface could be due to the simultaneous occurrence of several interdependent processes, such as the loss of stability of the coating with the formation of alternating areas of tensile and compressive stresses, diffusion of tungsten into the regions of compressive stresses, and relaxation of internal stresses by grain-boundary sliding with extrusion of grains and their conglomerates on the surface.

Sputtering of polished EUROFER97 steel: Surface structure modification and enrichment with tungsten and tantalum

Surface structure modification and enrichment with tungsten and tantalum were measured for polished EUROFER97 samples after exposure to a deuterium ion beam. Time-of-flight medium energy ion scattering and time-of-flight elastic recoil detection analysis were implemented for measuring atomic composition profiles. Atomic force microscopy and optical microscopy were used to investigate surface morphology. The deuterium particle fluence was varied between 1021 D/m2 and 1024 D/m2, projectile energy was 200 eV/D and exposure temperatures up to 1050 K were applied. The average fraction of tungsten plus tantalum to total metal content in the 2 nm closest to the sample surface was increased from an initial 0.0046 to 0.12 for the sample exposed to the highest fluence at room temperature. The enrichment was accompanied by an increase in surface roughness of one order of magnitude and grain dependent erosion of the material. The appearance of protrusions with heights up to approximately 40 nm after ion beam exposure at room temperature was observed on individual grains. Samples exposed to 1023 D/m2 at temperatures of 900 K and 1050 K displayed recrystallization and cracking while changes to the total surface fraction of tungsten and tantalum were limited to less than a factor of two compared to the sample exposed to the same fluence at room temperature.

An attempt to apply the inelastic thermal spike model to surface modifications of CaF2 induced by highly charged ions: comparison to swift heavy ions effects and extension to some others material

Surface damage appears on materials irradiated by highly charged ions (HCI). Since a direct link has been found between surface damage created by HCI with the one created by swift heavy ions (SHI), the inelastic thermal spike model (i-TS model) developed to explain track creation resulting from the electron excitation induced by SHI can also be applied to describe the response of materials under HCI which transfers its potential energy to electrons of the target. An experimental description of the appearance of the hillock-like nanoscale protrusions induced by SHI at the surface of CaF2 is presented in comparison with track formation in bulk which shows that the only parameter on which we can be confident is the electronic energy loss threshold. Track size and electronic energy loss threshold resulting from SHI irradiation of CaF2 is described by the i-TS model in a 2D geometry. Based on this description the i-TS model is extended to three dimensions to describe the potential threshold of appearance of protrusions by HCI in CaF2 and to other crystalline materials (LiF, crystalline SiO2, mica, LiNbO3, SrTiO3, ZnO, TiO2, HOPG). The strength of the electron–phonon coupling and the depth in which the potential energy is deposited near the surface combined with the energy necessary to melt the material defines the classification of the material sensitivity. As done for SHI, the band gap of the material may play an important role in the determination of the depth in which the potential energy is deposited. Moreover larger is the initial potential energy and larger is the depth in which it is deposited.

Solvent-exposed lipid tail protrusions depend on lipid membrane composition and curvature

The stochastic protrusion of hydrophobic lipid tails into solution, a subclass of hydrophobic membrane defects, has recently been shown to be a critical step in a number of biological processes like membrane fusion. Understanding the factors that govern the appearance of lipid tail protrusions is critical for identifying membrane features that affect the rate of fusion or other processes that depend on contact with solvent-exposed lipid tails. In this work, we utilize atomistic molecular dynamics simulations to characterize the likelihood of tail protrusions in phosphotidylcholine lipid bilayers of varying composition, curvature, and hydration. We distinguish two protrusion modes corresponding to atoms near the end of the lipid tail or near the glycerol group. Through potential of mean force calculations, we demonstrate that the thermodynamic cost for inducing a protrusion depends on tail saturation but is insensitive to other bilayer structural properties or hydration above a threshold value. Similarly, highly curved vesicles or micelles increase both the overall frequency of lipid tail protrusions as well as the preference for splay protrusions, both of which play an important role in driving membrane fusion. In multi-component bilayers, however, the incidence of protrusion events does not clearly depend on the mismatch between tail length or tail saturation of the constituent lipids. Together, these results provide significant physical insight into how system components might affect the appearance of protrusions in biological membranes, and help explain the roles of composition or curvature-modifying proteins in membrane fusion.

Why high cholesterol levels help hematological malignancies: role of nuclear lipid microdomains

BackgroundDiet and obesity are recognized in the scientific literature as important risk factors for cancer development and progression. Hypercholesterolemia facilitates lymphoma lymphoblastic cell growth and in time turns in hypocholesterolemia that is a sign of tumour progression. The present study examined how and where the cholesterol acts in cancer cells when you reproduce in vitro an in vivo hypercholesterolemia condition.MethodsWe used non-Hodgkin’s T cell human lymphoblastic lymphoma (SUP-T1 cell line) and we studied cell morphology, aggressiveness, gene expression for antioxidant proteins, polynucleotide kinase/phosphatase and actin, cholesterol and sphingomyelin content and finally sphingomyelinase activity in whole cells, nuclei and nuclear lipid microdomains.ResultsWe found that cholesterol changes cancer cell morphology with the appearance of protrusions together to the down expression of β-actin gene and reduction of β-actin protein. The lipid influences SUP-T1 cell aggressiveness since stimulates DNA and RNA synthesis for cell proliferation and increases raf1 and E-cadherin, molecules involved in invasion and migration of cancer cells. Cholesterol does not change GRX2 expression but it overexpresses SOD1, SOD2, CCS, PRDX1, GSR, GSS, CAT and PNKP. We suggest that cholesterol reaches the nucleus and increases the nuclear lipid microdomains known to act as platform for chromatin anchoring and gene expression.ConclusionThe results imply that, in hypercholesterolemia conditions, cholesterol reaches the nuclear lipid microdomains where activates gene expression coding for antioxidant proteins. We propose the cholesterolemia as useful parameter to monitor in patients with cancer.

The VP40 protein of Marburg virus exhibits impaired budding and increased sensitivity to human tetherin following mouse adaptation.

The Marburg virus VP40 protein is a viral matrix protein that spontaneously buds from cells. It also functions as an interferon (IFN) signaling antagonist by targeting Janus kinase 1 (JAK1). A previous study demonstrated that the VP40 protein of the Ravn strain of Marburg virus (Ravn virus [RAVV]) failed to block IFN signaling in mouse cells, whereas the mouse-adapted RAVV (maRAVV) VP40 acquired the ability to inhibit IFN responses in mouse cells. The increased IFN antagonist function of maRAVV VP40 mapped to residues 57 and 165, which were mutated during the mouse adaptation process. In the present study, we demonstrate that maRAVV VP40 lost the capacity to efficiently bud from human cell lines, despite the fact that both parental and maRAVV VP40s bud efficiently from mouse cell lines. The impaired budding in human cells corresponds with the appearance of protrusions on the surface of maRAVV VP40-expressing Huh7 cells and with an increased sensitivity of maRAVV VP40 to restriction by human tetherin but not mouse tetherin. However, transfer of the human tetherin cytoplasmic tail to mouse tetherin restored restriction of maRAVV VP40. Residues 57 and 165 were demonstrated to contribute to the failure of maRAVV VP40 to bud from human cells, and residue 57 was demonstrated to alter VP40 oligomerization, as assessed by coprecipitation assay, and to determine sensitivity to human tetherin. This suggests that RAVV VP40 acquired, during adaptation to mice, changes in its oligomerization potential that enhanced IFN antagonist function. However, this new capacity impaired RAVV VP40 budding from human cells. Filoviruses, which include Marburg viruses and Ebola viruses, are zoonotic pathogens that cause severe disease in humans and nonhuman primates but do not cause similar disease in wild-type laboratory strains of mice unless first adapted to these animals. Although mouse adaptation has been used as a method to develop small animal models of pathogenesis, the molecular determinants associated with filovirus mouse adaptation are poorly understood. Our study demonstrates how genetic changes that accrued during mouse adaptation of the Ravn strain of Marburg virus have impacted the budding function of the viral VP40 matrix protein. Strikingly, we find impairment of mouse-adapted VP40 budding function in human but not mouse cell lines, and we correlate the impairment with an increased sensitivity of VP40 to restriction by human but not mouse tetherin and with changes in VP40 oligomerization. These data suggest that there are functional costs associated with filovirus adaptation to new hosts and implicate tetherin as a filovirus host restriction factor.

Dynamics of β‐adrenergic/cAMP signaling and morphological changes in cultured astrocytes

The morphology of astrocytes, likely regulated by cAMP, determines the structural association between astrocytes and the synapse, consequently modulating synaptic function. β-Adrenergic receptors (β-AR), which increase cytosolic cAMP concentration ([cAMP]i ), may affect cell morphology. However, the real-time dynamics of β-AR-mediated cAMP signaling in single live astrocytes and its effect on cell morphology have not been studied. We used the fluorescence resonance energy transfer (FRET)-based cAMP biosensor Epac1-camps to study time-dependent changes in [cAMP]i ; morphological changes in primary rat astrocytes were monitored by real-time confocal microscopy. Stimulation of β-AR by adrenaline, noradrenaline, and isoprenaline, a specific agonist of β-AR, rapidly increased [cAMP]i (∼15 s). The FRET signal response, mediated via β-AR, was faster than in the presence of forskolin (twofold) and dibutyryl-cAMP (>35-fold), which directly activate adenylyl cyclase and Epac1-camps, respectively, likely due to slow entry of these agents into the cytosol. Oscillations in [cAMP]i have not been recorded, indicating that cAMP-dependent processes operate in a slow time domain. Most Epac1-camps expressing astrocytes revealed a morphological change upon β-AR activation and attained a stellate morphology within 1 h. The morphological changes exhibited a bell-shaped dependency on [cAMP]i . The 5-10% decrease in cell cross-sectional area and the 30-50% increase in cell perimeter are likely due to withdrawal of the cytoplasm to the perinuclear region and the appearance of protrusions on the surface of astrocytes. Because astrocyte processes ensheath neurons, β-AR/cAMP-mediated morphological changes can modify the geometry of the extracellular space, affecting synaptic, neuronal, and astrocyte functions in health and disease.

Effect of atomic hydrogen bombardment on the surface conductivity of polycrystalline diamond films

The surface conductivity of polished polycrystalline diamond films after atomic hydrogen bombardment for different time was compared and the carrier transport characteristic beneath the H-terminated diamond film surface was investigated correspondingly. It is found that, as the bombardment time increases, the surface roughness of diamond films first decreases due to disappearance of scratches, and then increases because of appearance of protrusions produced by plasma preferentially etching. Meanwhile the total CH bonding concentration on the diamond surface increases gradually until it is saturated when the bombardment time is up to 30min. The almost invariable carrier density is obtained for all samples treated for different time, which indicates the monohydride (CH) mode responsible for surface conductivity forms when hydrogen treatment starts. While for the carrier mobility, it shows the inverse trend with change of the surface roughness. A model based on the surface roughness scattering was proposed to explain the relationship between the surface conductivity and roughness. Combining with the carrier mobility and density, the lowest square resistance of 13.85kΩ is obtained for polycrystalline diamond film when it is treated for 30min. It is speculated that the surface conductivity can be further enhanced by reducing the surface roughness.

Study of the porous structure of white chocolate by confocal Raman microscopy

AbstractConfocal Raman microscopy has been shown to be a useful technique for investigation of white chocolate surfaces. The appearance of protrusions and pores, and the distribution of fat, sucrose, and milk powder at and below the surface of white chocolate pralines were investigated using confocal Raman microscopy. Raman horizontal and depth scans showed that the protrusions and pores continue at least 10 µm into the chocolate shell and that some protrusions and channels mainly consist of fat, while some consisted of a fat layer, leaving a hollow space underneath. Further, the pores and their continuing channels consisted of nothing but air. These findings indicate that the protrusions might be connected to channels where we suggest a pressure driven convective flow of liquid fat from within the chocolate matrix that, depending on temperature, moves up to the surface or goes back into the matrix, leaving an empty pore with a shell of fat at the surface, which in some cases collapse and leaves a hollow pore and channel. Therefore, these findings support that the protrusions could be connected to oil migration in chocolate and, thus, further to fat bloom development.Practical applications: Confocal Raman microscopy can be used to investigate the local distribution of different components in white chocolate. This technique offers the possibility to acquire the local distribution of different components within the sample, with a resolution down to the optical diffraction limit. Further, the analysis can be performed at ambient conditions, without requiring any special sample preparation or marker molecules. The results obtained by using this technique suggest that specific surface imperfections on chocolate could be part of a network of pore structures at and beneath the chocolate surface, which could be related to oil migration and thus, to fat bloom formation.

Phase Transitions of the Coupled Membrane-Cytoskeleton Modify Cellular Shape

Formation of protrusions and protein segregation on the membrane is of a great importance for the functioning of the living cell. This is most evident in recent experiments that show the effects of the mechanical properties of the surrounding substrate on cell morphology. We propose a mechanism for the formation of membrane protrusions and protein phase separation, which may lay behind this effect. In our model, the fluid cell membrane has a mobile but constant population of proteins with a convex spontaneous curvature. Our basic assumption is that these membrane proteins represent small adhesion complexes, and also include proteins that activate actin polymerization. Such a continuum model couples the membrane and protein dynamics, including cell-substrate adhesion and protrusive actin force. Linear stability analysis shows that sufficiently strong adhesion energy and actin polymerization force can bring about phase separation of the membrane protein and the appearance of protrusions. Specifically, this occurs when the spontaneous curvature and aggregation potential alone (passive system) do not cause phase separation. Finite-size patterns may appear in the regime where the spontaneous curvature energy is a strong factor. Different instability characteristics are calculated for the various regimes, and are compared to various types of observed protrusions and phase separations, both in living cells and in artificial model systems. A number of testable predictions are proposed.

LEEM and XPEEM studies of C-AFM induced surface modifications of thermally grown SiO 2

The process of local anodic oxidation, where a positive voltage is applied between a sample and a conducting probe, is well understood. Here, conducting atomic force microscope (C-AFM) induced surface modifications of thermally grown SiO 2 are investigated for opposite (i.e. negative) sample bias. Also at this polarity, surprisingly, the appearance of protrusions is observed. To obtain information on the nature of these protrusions, low-energy electron microscopy (LEEM) and X-ray photoemission electron microscopy (XPEEM) measurements were performed. Photoemission spectra reveal that the structures formed by C-AFM are chemically homogeneous, and that they are caused by the growth of additional SiO 2 on the sample surface.

Modulation of the Characteristics of Intense Picosecond Stimulated Emission from GaAs

Intense picosecond stimulated emission from the face of a thin GaAs film is studied. The emission is observed when GaAs is pumped with high-power picosecond optical pulses. It is found that the dependences of the emission energy on the photon energy, the picosecond delay between two pump pulses, and the distance between the active region and the face are modulated. Modulation is taken to mean the appearance of protrusions or peaks in any of the mentioned dependences. The modulation parameters for the dependences under consideration are found to be related by expressions that make it possible to suggest the following. The modulation of characteristics is caused by a common (not yet conclusively identified) mechanism of self-modulation of the emission spectrum. This mechanism is related to an ultrafast nonlinear interaction between a highly photoexcited semiconductor and the pump radiation and stimulated emission. There is indirect evidence that this mechanism also gives rise to an amplitude modulation of the emission in a picosecond time interval.

Exocytosis in human salivary glands visualized by high-resolution scanning electron microscopy.

The luminal membrane of salivary acinar cells creates a specialized cell surface area that accepts exocytosis and undergoes dynamic changes during secretion. These changes were visualized three-dimensionally from both the inside and outside of the cell in human parotid and submandibular glands, by application of in vitro secretory stimulation and then of OsO4 maceration to remove cytoplasmic organelles by varying degrees. In control glands treated without secretagogues, the luminal surface of serous acinar cells bore well-developed microvilli with only an occasional incidence of exocytotic profiles. Following treatment with the beta-adrenergic agonist, isoproterenol, considerable shortening and loss of microvilli occurred along the luminal membrane where, on its cytoplasmic side, many protuberances of sizes similar to or smaller than those of single secretory granules (approximately 1 micron in diameter) appeared. The cytoplasmic surface of these protuberances exhibited small vesicles (approximately 100-150 nm in diameter) that, by transmission electron microscopy, were shown to be coated pits or vesicles present on or around the exocytosed granule membranes. Treatment of tissues with the muscarinic agonist carbachol also caused a decrease of microvilli and the appearance of protrusions at the luminal membrane. However, unlike isoproterenol treatment, many of these protrusions were devoid of small pits or vesicles and were much larger than a single secretory granule. These results indicate that (1) secretory stimulation causes the dynamic transformation of microvilli at the luminal membrane, where granule docking and membrane fusion take place, and (2) after fusion, the exocytosed membranes are processed differently, by coated pit/vesicle mediated or non-mediated mechanisms, according to the autonomic receptor control.

Rearrangement of intramembranous particles and fusion promoted in chicken erythrocytes by intracellular Ca 2+

Ca 2+ was introduced into fresh and ATP-depleted chicken erythrocytes through the aid of the ionophore A-23187. Intracellular Ca 2+ (10–40 mM) induced fusion in ATP-depleted cells after 30–60 min incubation at 37°C, but not in fresh cells. Fresh cells underwent a higher degree of haemolysis than ATP-depleted cells after accumulation of Ca 2+. Uptake of Ca 2+ was the same in these two systems. Intracellular Ca 2+ induced rearrangement of intramembranous particles, as revealed by freeze-etching studies. The intramembranous particles in the protoplasmic face of fractured membranes obtained from fresh cells incubated with 1 mM of Ca 2+ were more scattered and their density was lower than in control cells. Incubation with higher concentrations of Ca 2+ (10–40 mM) induced transient changes in the intramembranous particles' density with the appearance of protrusions and depressions on the protoplasmic and exoplasmic faces of the fractured membranes, respectively. These effects were reversible upon removal of Ca 2+ by washing the cells with ethyleneglycol bis(α- aminoethylether)-N,N′- tetraacetic acid; rearrangement of intramembranous particles was less evident after accumulation of Ca 2+ in ATP-depleted cells, whose fractured membranes did not contain any protrusions or depressions. Transferring Ca 2+-loaded cells to the cold caused the formation of large smooth areas devoid of intramembranous particles in the protoplasmic face of the fractured membranes. Cells containing Ca 2+ appeared spherical, and removal of Ca 2+ restored the normal oval shape of chicken erythrocytes.

Fine structural studies of rat adrenal cortices following prostaglandin administration.

Histological and fine structural studies of adrenal cortices were performed on male Sprague-Dawley rats which had been given intravenous injections of prostaglandin E1 or E2. It was found that there were increased numbers of intracellular lipid droplets, free ribonucleoprotein particles, cholesterol ester clefts and coated vesicles of both the small and large varieties. A reorganization of the internal mitochondrial membranes and the appearance of protrusions of parenchymal cytoplasm into the sinusoidal lumina accompanied by vasodilation were also observed. These alterations are not typical of those observed following exogenous ACTH administration and are therefore considered to be prostaglandin-induced.

ORTHODONTIC FACIAL ORTHOMORPHIA.IMPORTANCE OF DIFFERENTIATION IN CASES OF APPARENT MANDIBULAR PROTRUSION.

Quite a little has been written on the etiology and treatment of cases presenting the appearance of protrusion of the mandible, the chin-cap treatment being recommended in young subjects and the removal of sections from each side of the mandible in older patients, and of late much has been written regarding the technic of this latter operation. In a recent article Dr. E. H. Angle mentions a case in which this operation was successfully done in St. Louis 1 and tells of a failure having been made in New Orleans. 2 I have heard rumors in New Orleans concerning this failure, but have never seen the case. Much has been written about treatment and a little about etiology, but apparently very little thought has been given to diagnosis, and the object of this brief paper is to emphasize the importance of a correct diagnosis on which to base an intelligent prescription. It