Low-energy scanning transmission electron microscopy applied to ice-embedded biological macromolecules.

In this report, we applied annular bright-field and annular dark-field low-energy (30 keV) scanning transmission electron microscopy imaging to a vitreous ice-embedded biological macromolecule, T4 phage, to investigate the applicability of these methods for morphological investigation and sample screening. Multiple camera lengths were examined to find the optimal acceptance angle for both modes. Image clarity differed substantially between the modes, with the presence of ice also strongly influencing the quality of acquired micrographs.

Interpretation of mean free path values derived from off-axis electron holography amplitude measurements.

In this work, we have explored the factors which govern mean free path values obtained from off-axis electron holography measurements. Firstly, we explore the topic from a theoretical perspective, and show that the mean amplitude reconstructed from off-axis holograms is due to the coherent portion of the direct, central object-transmitted beam only - it is not affected by the presence or absence of other scattered beams. Secondly, we present a detailed experimental study which compares mean free path values obtained from hologram sideband, centreband, EELS, and TEM measurements as a function of optical collection angle and energy-loss-filtering.

Low-energy in-line electron holographic imaging of vitreous ice-embedded small biomolecules using a modified scanning electron microscope.

Cryo-electron microscopy (cryo-EM) has become the method of choice in the field of structural biology, owing to its unique ability to deduce structures of vitreous ice-embedded, hydrated biomolecules over a wide range of structural resolutions. As cryo-transmission electron microscopes (cryo-TEM) become increasingly specialised for high, near-atomic resolution studies, operational complexity and associated costs serve as significant barriers to widespread usability and adoptability. To facilitate the expansion and accessibility of the cryo-EM method, an efficient, user-friendly means of imaging vitreous ice-embedded biomolecules has been called for.

Improved sample dispersion in cryo-EM using "perpetually-hydrated" graphene oxide flakes.

For many macromolecular complexes, the inability to uniformly disperse solubilized specimen particles within vitreous ice films precludes their analysis by cryo-electron microscopy (cryo-EM). Here, we introduce a sample preparation process using "perpetually-hydrated" graphene oxide flakes as particle support films, and report vastly improved specimen dispersion. The new method introduced in this study incorporates hydrated graphene oxide flakes into a standard sample preparation regime, without the need for additional tools or devices, making it a cost-effective and easily adoptable alternative to currently available sample preparation approaches.

Improved sample dispersion in cryo-EM using "perpetually-hydrated" graphene oxide flakes.

For many macromolecular complexes, the inability to uniformly disperse solubilized specimen particles within vitreous ice films precludes their analysis by cryo-electron microscopy (cryo-EM). Here, we introduce a sample preparation process using "perpetually-hydrated" graphene oxide flakes as particle support films, and report vastly improved specimen dispersion. Furthermore, we provide evidence that the presence of graphene oxide flakes in vitreous ice results in a significant reduction in electron beam-induced specimen decomposition.

Development of a SEM-based low-energy in-line electron holography microscope for individual particle imaging.

A new SEM-based in-line electron holography microscope has been under development. The microscope utilizes conventional SEM and BF-STEM functionality to allow for rapid searching of the specimen of interest, seamless interchange between SEM, BF-STEM and holographic imaging modes, and makes use of coherent low-energy in-line electron holography to obtain low-dose, high-contrast images of light element materials. We report here an overview of the instrumentation and first experimental results on gold nano-particles and carbon nano-fibers for system performance tests.

Water without windows: Evaluating the performance of open cell transmission electron microscopy under saturated water vapor conditions, and assessing its potential for microscopy of hydrated biological specimens.

We have performed open cell transmission electron microscopy experiments through pure water vapor in the saturation pressure regime (>0.6 kPa), in a modern microscope capable of sub-Å resolution. We have systematically studied achievable pressure levels, stability and gas purity, effective thickness of the water vapor column and associated electron scattering processes, and the effect of gas pressure on electron optical resolution and image contrast.

Graphene specimen support technique for low voltage STEM imaging.

The scanning transmission electron microscopy (STEM) mode of today's field emission scanning electron microscopes enables sub-nanometer resolution imaging. Graphene is a single-atom thick, electrically conductive material, making it an excellent specimen support for the low voltage STEM imaging of nanometer-sized objects such as viruses. Here we present low voltage STEM images of bacteriophage T4 recorded on highly cleaned graphene films.

Signatures of bond formation and bond scission dynamics in dissociative electron attachment to methane.

We present a combined experimental and theoretical investigation of the dynamics and angular dependence of dissociative electron attachment to methane. We show that a triply degenerate (T2) Feshbach resonance is responsible for the broad 10 eV dissociation peak in methane. This resonance alone is shown to correlate asymptotically to the various dissociation channels observed experimentally.

A momentum imaging microscope for dissociative electron attachment.

We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere.

Imaging the molecular dynamics of dissociative electron attachment to water.

Momentum imaging experiments on dissociative electron attachment (DEA) to a water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

Angular correlation between photoelectrons and auger electrons from K-shell ionization of neon.

We have used cold target recoil ion momentum spectroscopy to study the continuum correlation between the photoelectron of core-photoionized neon and the subsequent Auger electron. We observe a strong angular correlation between the two electrons. Classical trajectory Monte Carlo calculations agree quite well with the photoelectron energy distribution that is shifted due to the potential change associated with Auger decay.

Interference in the collective electron momentum in double photoionization of H2.

We investigate single-photon double ionization of H(2) by 130 to 240 eV circularly polarized photons. We find a double slitlike interference pattern in the sum momentum of both electrons in the molecular frame which survives integration over all other degrees of freedom. The difference momentum and the individual electron momentum distributions do not show such a robust interference pattern.

The simplest double slit: interference and entanglement in double photoionization of H2.

The wave nature of particles is rarely observed, in part because of their very short de Broglie wavelengths in most situations. However, even with wavelengths close to the size of their surroundings, the particles couple to their environment (for example, by gravity, Coulomb interaction, or thermal radiation). These couplings shift the wave phases, often in an uncontrolled way, and the resulting decoherence, or loss of phase integrity, is thought to be a main cause of the transition from quantum to classical behavior.

Factors determining clockwise and counterclockwise conduction patterns in atrial reentrant tachycardias: a rabbit model of atrial flutter.

Introduction: In the development of atrial flutter due to reentry, the crista terminalis is supposed to pose a conduction barrier, but the role of its longitudinal conduction in determining the propagation pattern of the reentrant impulse is not known. In rabbit right atrial preparations, we induced reentrant atrial tachycardias and examined the effects of transverse section of the crista terminalis on the development and conduction patterns of arrhythmias.

Methods And Results: Right atrial preparations from 12 albino rabbits were placed endocardial surface down in a chamber with an array of 48 bipolar electrodes to draw activation maps.

Prevalence and clinical features of hepatitis delta virus infection in the Miyako Islands, Okinawa, Japan.

The aims of this study were twofold: (1) to determine the prevalence and clinical features of hepatitis delta virus (HDV) infection among subjects positive for hepatitis B surface antigen (HBsAg) living in the Miyako Islands, Okinawa Prefecture, Japan, and (2) to clarify the relationship between HDV-RNA level and severity of HDV-related liver disease. One hundred and ninety-nine HBsAg-positive subjects (123 asymptomatic carriers [ASCs], 3 patients with acute hepatitis [AH], 50 patients with chronic hepatitis [CH], 15 patients with liver cirrhosis [LC], and 8 patients with hepatocellular carcinoma [HCC], were tested for antibody to HDV (anti-HDV) by radioimmunoassay. Anti-HDV-positive individuals were examined to determine semi-quantified HDV-RNA level by polymerase chain reaction (PCR).

Determination of hepatitis delta virus (HDV)-RNA in asymptomatic cases of HDV infection.

Objectives: To assess the frequency of hepatitis delta virus (HDV) viremia in asymptomatic cases of HDV infection and the clinical significance of the HDV viremia, we conducted a cross-sectional, community-based study.

Methods: Of 2207 examinees, 210 (9.5%) were found to be positive for hepatitis B surface antigen (HBsAg).

Seroepidemiological study on hepatitis delta virus infection in the Irabu Islands, Okinawa, Japan.

A seroepidemiological study was performed to clarify the prevalence of hepatitis delta virus (HDV) infection among the general population in the Irabu islands, Okinawa, Japan. Of 2028 healthy people examined who had received their annual health check-up in 1994-95, 195 (9.6%) were positive for hepatitis B surface antigen (HBsAg).

Effects of antiarrhythmic agents and Mg2+ on aconitine-induced arrhythmias.

The effects of antiarrhythmic agents, including Classes I and IV and 3-10 mM Mg2+ on aconitine-induced arrhythmias were examined using a conventional microelectrode and patch clamp method in Langendorff-perfused rabbit hearts and isolated guinea-pig ventricular myocytes. Intracoronary application of 0.1 microM aconitine induced polymorphic ventricular tachycardia (PVT) which continued for more than 60 minutes.

Electrophysiological effects of clentiazem, a new Ca2+ antagonist, on rabbit hearts.

Electrophysiological effects of clentiazem, a new 1,5-benzothiazepine type Ca(2+) antagonist, were examined in comparison with those of diltiazem in excised rabbit heart preparations. In Langendorff-perfused hearts electrically driven at basic cycle lengths of 400-500 ms, clentiazem (10(-8)-10(-6)M) and diltiazem (10(-8)-10(-6)M) caused a concentration-dependent prolongation of the atrio-His bundle conduction time (A-H interval) without affecting the His bundle-ventricular conduction time (H-V interval). The effects of clentiazem were equivalent to those of diltiazem.

Dual effects of external magnesium on action potential duration in guinea pig ventricular myocytes.

Effects of extracellular magnesium (Mg2+) on action potential duration (APD) and underlying membrane currents in guinea pig ventricular myocytes were studied by using the whole cell patch-clamp method. Increasing external Mg2+ concentration [Mg2+]o) from 0.5 to 3 mM produced a prolongation of APD at 90% repolarization (APD90), whereas 5 and 10 mM Mg2+ shortened it.

Role for ATP-sensitive K+ channel in the development of A-V block during hypoxia.

The role of the ATP-sensitive K+ channel (IK,ATP) in the development of A-V block during hypoxic interventions was studied using Langendorff perfused rabbit hearts, multicellular rabbit A-V nodal preparations and single guinea-pig ventricular myocytes. With the Langendorff perfused hearts, hypoxic perfusion (PO2 not equal to 40 mmHg) for 30 min caused slowing of the sinus rate and prolongation of the A-H interval without the appearance of blocked beats. Substrate-free hypoxic perfusion induced second or third degree A-V block in 8/10 hearts and substrate-free hypoxic perfusion plus 2-deoxyglucose (5 mM) produced third degree A-V block in 6/6 preparations.

Effects of magnesium on polymorphic ventricular tachycardias induced by aconitine.

We examined the effects of Mg2+ on aconitine-induced polymorphic ventricular tachycardias (PVT) in excised rabbit hearts under Langendorff perfusion and in Purkinje-muscle preparations. Local electrograms using bipolar electrodes and transmembrane potentials with the microelectrode technique were recorded from Langendorff hearts and Purkinje-muscle preparations, respectively. In Langendorff preparations, intracoronary application of 0.

Rate-dependent effects of sematilide on action potential duration in isolated guinea pig ventricular myocytes.

We examined the underlying mechanism for rate-dependent effects of sematilide on action potential duration (APD) in guinea pig ventricular myocytes. Sematilide at 10 microM or higher concentrations caused prolongation of the APD without changing other electrical parameters at a stimulation rate of 0.2 Hz.