Quantitative Measurement of Transmitters in Individual Vesicles in the Cytoplasm of Single Cells with Nanotip Electrodes

The quantification of vesicular transmitter content is important for studying the mechanisms of neurotransmission and malfunction in disease, and yet it is incredibly difficult to measure the tiny amounts of neurotransmitters in the attoliter volume of a single vesicle, especially in the cell environment. We introduce a novel method, intracellular vesicle electrochemical cytometry. A nanotip conical carbon‐fiber microelectrode was used to electrochemically measure the total content of electroactive neurotransmitters in individual nanoscale vesicles in single PC12 cells as these vesicles lysed on the electrode inside the living cell. The results demonstrate that only a fraction of the quantal neurotransmitter content is released during exocytosis. These data support the intriguing hypothesis that the vesicle does not open all the way during the normal exocytosis process, thus resulting in incomplete expulsion of the vesicular contents.     

Large-scale flow structures in a planar offset attaching jet with a co-flowing wall jet

Conditional averaging techniques were used to examine the periodic motions that were observed in flows consisting of an offset planar jet and a co-flowing planar wall jet. The offset jet is one jet height (H_j) away from the wall and has a Reynolds number of approximately 40, 000, based on H_j and flow-rate averaged velocity U_o; for the co-flowing jets, different heights (i.e., 0.18H_j and 0.5H_j) and velocities (i.e., 0.56U_o and 0.36U_o) were considered. The flows had periodic motions with frequencies fH_j/U_o = 0.28 and 0.49 or fH_c/U_o = 0.23 and 0.25, where H_c is the distance between the jets. The periodic motions were present in both the inner shear layer of the offset jet above the re-circulation region and the outer shear layer of the wall jet below the re-circulation region. The motions from the inner shear layer of the offset jet persisted in the shear layer that formed downstream of the re-circulating region. There were periodic motions in the outer shear layer of the offset jet particularly in the flow with the smaller wall jet. The relative contribution of the motions to the total fluctuations increased as the flow evolved downstream reaching a maximum approximately 4H_c downstream of the flow exit. The relative contribution of the periodic motions to the turbulent fluctuations was similar in the two flows but the periodic motions had a much larger impact on the near-wall velocity and pressure fluctuations in the flow with the smaller wall jet due to the trajectory of the periodic structures, the distance of the periodic structures to the wall and the size of these structures.     

Hardness and elastic modulus of zircon as a function of heavy-particle irradiation dose: I. In situ α-decay event damage

Abstract

For a natural single crystal of zircon, ZrSiO₄, from Sri Lanka, exhibiting zonation in U and Th contents, the hardness and elastic modulus have been determined as a function of α-decay dose using a mechanical properties microprobe (MPM). The zones vary in thickness from one to hundreds of micrometers, and have uranium and thorium concentrations such that the α-decay dose varies between 2 × 10¹⁵ and 1 × 10¹⁶ α-decay events/mg (0.15 to 0.65 dpa, displacement per atom). The transition from the crystalline to the aperiodic metamict state occurs over this dose range. For a traverse of 75 indent pairs across layers sampling a large portion of the crystalline-to-metamict transition (3.7 × 10¹⁵ to 9.7 × 10¹⁵ α-decay events/mg) both the hardness and elastic modulus decrease linearly with increasing α-decay dose. The radiation-induced softening follows a behavior similar to other radiation-induced changes, that is with the expansion of the unit cell parameters there is a decrease in density, birefringence, hardness and bulk modulus.     

Investigation of temperature parallel simulated annealing for optimizing continuous functions with application to hyperspectral tomography

The simulated annealing (SA) algorithm is a well-established optimization technique which has found applications in many research areas. However, the SA algorithm is limited in its application due to the high computational cost and the difficulties in determining the annealing schedule. This paper demonstrates that the temperature parallel simulated annealing (TPSA) algorithm, a parallel implementation of the SA algorithm, shows great promise to overcome these limitations when applied to continuous functions. The TPSA algorithm greatly reduces the computational time due to its parallel nature, and avoids the determination of the annealing schedule by fixing the temperatures during the annealing process. The main contributions of this paper are threefold. First, this paper explains a simple and effective way to determine the temperatures by applying the concept of critical temperature (T_C). Second, this paper presents systematic tests of the TPSA algorithm on various continuous functions, demonstrating comparable performance as well-established sequential SA algorithms. Third, this paper demonstrates the application of the TPSA algorithm on a difficult practical inverse problem, namely the hyperspectral tomography problem. The results and conclusions presented in this work provide are expected to be useful for the further development and expanded applications of the TPSA algorithm.     

Trends in computational simulations of electrochemical processes under hydrodynamic flow in microchannels

Computational modeling and theoretical simulations have recently become important tools for the development, characterization, and validation of microfluidic devices. The recent proliferation of commercial user-friendly software has allowed researchers in the microfluidics community, who might not be familiar with computer programming or fluid mechanics, to acquire important information on microsystems used for sensors, velocimetry, detection for microchannel separations, and microfluidic fuel cells. We discuss the most popular computational technique for modeling these systems—the finite element method—and how it can be applied to model electrochemical processes coupled with hydrodynamic flow in microchannels. Furthermore, some of the limitations and challenges of these computational models are also discussed.     

Amorphization of nanocrystalline monoclinic ZrO(2) by swift heavy ion irradiation

Bulk ZrO(2) polymorphs generally have an extremely high amorphization tolerance upon low energy ion and swift heavy ion irradiation in which ballistic interaction and ionization radiation dominate the ion-solid interaction, respectively. However, under very high-energy irradiation by 1.33 GeV U-238, nanocrystalline (40-50 nm) monoclinic ZrO(2) can be amorphized. A computational simulation based on a thermal spike model reveals that the strong ionizing radiation from swift heavy ions with a very high electronic energy loss of 52.2 keV nm(-1) can induce transient zones with temperatures well above the ZrO(2) melting point. The extreme electronic energy loss, coupled with the high energy state of the nanostructured materials and a high thermal confinement due to the less effective heat transport within the transient hot zone, may eventually be responsible for the ionizing radiation-induced amorphization without transforming to the tetragonal polymorph. The amorphization of nanocrystalline zirconia was also confirmed by 1.69 GeV Au ion irradiation with the electronic energy loss of 40 keV nm(-1). These results suggest that highly radiation tolerant materials in bulk forms, such as ZrO(2), may be radiation sensitive with the reduced length scale down to the nano-metered regime upon irradiation above a threshold value of electronic energy loss.     

Dissociation of multiply charged negative ions for hirudin (54–65), fibrinopeptide B, and insulin A (oxidized)

Collision-induced dissociation (CID) was performed on multiply deprotonated ions from three commercial peptides: hirudin (54-65), fibrinopeptide B, and oxidized insulin chain A. Ions were produced by electrospray ionization in a Fourier transform ion cyclotron resonance mass spectrometer. Each of these peptides contains multiple acidic residues, which makes them very difficult to ionize in the positive mode. However, the peptides deprotonate readily making negative ion studies a viable alternative. The CID spectra indicated that the likely deprotonation sites are acidic residues (aspartic, glutamic, and cysteic acids) and the C-terminus. The spectra are rife with c, y, and internal ions, although some a, b, x, and z ions form. Many of the fragment ions were formed from cleavage adjacent to acidic residues, both N- and C-terminal to the acidic site. In addition, neutral loss (e.g., NH3, CH3, H2O, and CO2) was prevalent from both the parent ions and from fragment ions. These neutral eliminations were often indicative of specific amino acid residues. The fragmentation patterns from several charge states of the parent ions, when combined, provide significant primary sequence information. These results suggest that negative mode CID of multiply deprotonated ions provides useful structural information and can be worthwhile for highly acidic peptides that do not form positive ions in abundance.     

螺旋波激发甲烷等离子体光谱诊断

利用螺旋波激发等离子体化学气相沉积(LPP-CVD)技术,以甲烷和氦气为反应气体产生等离子体.通过采集到甲烷的可见光到紫外发射光谱,对甲烷等离子体进行原位诊断,发现存在CH、Ha及Hβ等碎片粒子的光辐射,同时,分析了不同入射功率、气压下CH粒子以及Hβ、Hγ的相对强度变化情况.结果表明:CH粒子的相对强度随着射频功率是先增大而后减小,随工作气压的增大而逐渐减小;随气压及功率的增加,Hβ、Hγ相对强度变化的总体趋势都是先增加而后减小的.     

Relative quantification of cellular sections with molecular depth profiling ToF-SIMS imaging

We report the use of secondary ion mass spectrometry (SIMS) imaging to quantify the relative difference in the amount of lipid between two sections, the plasma membrane and the cytoplasm, of single cells from two different populations. Cells were each labeled with lipophillic dyes, frozen, fractured and analyzed in a ToF-SIMS mass spectrometer equipped with a 40 keV C₆₀⁺ ion source. In addition to identifying cells from separate populations, the lipophilic dyes can be used as a marker for the outer leaflet of the cell membrane and therefore as a depth finder. Here, we show that it is possible to compare the amount of lipids with particular headgroups in the cell membrane of a treated cell to the membrane of a control cell. Following erosion of the cell membranes, the amount of the two specific lipid head groups in the cytoplasm of the treated cell can be compared to those lipids in a control cell. Here we take the first step in this experimental design and display the ability to analyze multiple sections of frozen cells following a single fracture.