In recent work with large high-symmetry viruses, single-particle electron cryomicroscopy (cryo-EM) has achieved the determination of near-atomic-resolution structures by allowing direct fitting of atomic models into experimental density maps. However, achieving this goal with smaller particles of lower symmetry remains challenging. Using a newly developed single electron-counting detector, we confirmed that electron beam-induced motion substantially degrades resolution, and we showed that the combination of rapid readout and nearly noiseless electron counting allow image blurring to be corrected to subpixel accuracy, restoring intrinsic image information to high resolution (Thon rings visible to ∼3 A). Using this approach, we determined a 3.3-A-resolution structure of an ∼700-kDa protein with D7 symmetry, the Thermoplasma acidophilum 20S proteasome, showing clear side-chain density. Our method greatly enhances image quality and data acquisition efficiency-key bottlenecks in applying near-atomic-resolution cryo-EM to a broad range of protein samples.

Electron counting and beam-induced motion correction enable near-atomic-resolution single-particle cryo-EM

https://diyhpl.us/~nmz787/pdf/How_cryo-EM_is_revolutionizing_structural_biology.pdf

How cryo-EM is revolutionizing structural biology

https://www.cell.com/cell/pdf/S0092-8674(15)00369-4.pdf

Single-Particle Cryo-EM at Crystallographic Resolution

Since the development of the first chemoresistive metal oxide based gas sensors, transducers with innovative properties have been prepared by a variety of wet- and dry-deposition methods. Among these, direct assembly of nanostructured films from the gas phase promises simple fabrication and control and with the appropriate synthesis and deposition methods nm to μm thick films, can be prepared. Dense structures are achieved by tuning chemical or vapor deposition methods whereas particulate films are obtained by deposition of airborne, mono- or polydisperse, aggregated or agglomerated nanoparticles. Innovative materials in non-equilibrium or sub-stoichiometric states are captured by rapid cooling during their synthesis. This Review presents some of the most common chemical and vapor-deposition methods for the synthesis of semiconductor metal oxide based detectors for chemical gas sensors. In addition, the synthesis of highly porous films by novel aerosol methods is discussed. A direct comparison of structural and chemical properties with sensing performance is given.

Semiconductor Gas Sensors: Dry Synthesis and Application

Although electron cryo-microscopy (cryo-EM) single-particle analysis has become an important tool for structural biology of large and flexible macro-molecular assemblies, the technique has not yet reached its full potential. Besides fundamental limits imposed by radiation damage, poor detectors and beam-induced sample movement have been shown to degrade attainable resolutions. A new generation of direct electron detectors may ameliorate both effects. Apart from exhibiting improved signal-to-noise performance, these cameras are also fast enough to follow particle movements during electron irradiation. Here, we assess the potentials of this technology for cryo-EM structure determination. Using a newly developed statistical movie processing approach to compensate for beam-induced movement, we show that ribosome reconstructions with unprecedented resolutions may be calculated from almost two orders of magnitude fewer particles than used previously. Therefore, this methodology may expand the scope of high-resolution cryo-EM to a broad range of biological specimens.

DOI: http://dx.doi.org/10.7554/eLife.00461.001

Ribosome structures to near-atomic resolution from thirty thousand cryo-EM particles

Experimental observation of the improvement in MTF from backthinning a CMOS direct electron detector

A novel floating inductance simulator, based on second generation current conveyors, is presented The circuit shows the capability of regulation and, in theory, cancellation of the undesired inductance series resistance, with consequent increase in the low frequency operating range Simulation results are included to prove the effectiveness of this solution

CCII-based floating inductance simulator with compensated series resistance

In this paper, a novel current mode CMOS four-quadrant analog multiplier circuit is presented. The multiplication is implemented by four translinear loops with MOS transistors operating in weak inversion. Information carrying signals are differential balanced currents. The multiplier circuit has been implemented in a test chip in a standard 0.35 /spl mu/m CMOS technology. The experimental measurements (dc bias current of 250 nA and a power supply of 2.0 V) show a bandwidth of 200 kHz and a THD figure value lower than 0.9 %. The multiplier features a wide signal dynamic range and linearity, low power consumption (the maximum power consumption is of 5.5/spl middot/10/sup -6/ W) and very low area (18.7 /spl middot/10/sup -3/ mm/sup 2/). The multiplier is suitable for a wide range of analog signal processing applications. Due to the low power and silicon area consumption, scalability and modularity can be also easily integrated in massive parallel systems.

A novel current-mode very low power analog CMOS four quadrant multiplier

A new current mode building block named voltage and current gain second generation current conveyor (VCG-CCII) is introduced. The voltage and current buffers of the standard CCII are replaced by voltage and current amplifiers with tunable gains so to obtain an extremely flexible and versatile building block. The VCG-CCII can be used in place of the standard CCII in impedance conversion applications so to utilize only one active component. A circuit implementation in a standard 0.35 μm CMOS process is presented and used to multiply, as an example, a 10 pF capacitor by a factor tunable from 1 up to about 3100, achieving a capacitance multiplication for more than 6 decades frequency range (from 0.15 to 865 KHz for the highest multiplication factor).

The VCG-CCII: a novel building block and its application to capacitance multiplication

In this brief, we describe how, using low-voltage low-power second-generation current conveyors, it is possible to simulate the frequency behavior of high capacitances and inductances by utilizing only elements suitable for an integrated implementation. The effect of current conveyor nonidealities has been taken into account. The simulated inductances and capacitances have been utilized, as an example, in the design of a fully integrated bandpass filter. PSPICE simulations, performed employing a standard CMOS technology (ALCATEL Mietec 0.5 /spl mu/m) and showing good performance of the presented circuits, are also reported.

Nicola Guerrini

Papers

Experimental observation of the improvement in MTF from backthinning a CMOS direct electron detector

CCII-based floating inductance simulator with compensated series resistance

A novel current-mode very low power analog CMOS four quadrant multiplier

The VCG-CCII: a novel building block and its application to capacitance multiplication

High-valued passive element simulation using low-voltage low-power current conveyors for fully integrated applications