Compact Particle Research Articles

Ptychographic measurements of ultrahigh-intensity laser–plasma interactions

The extreme intensities now delivered by femtosecond lasers make it possible to drive and control relativistic motion of charged particles with light1, opening a path to compact particle accelerators2, 3 and coherent X-ray sources4, 5. Accurately characterizing the dynamics of ultrahigh-intensity laser–plasma interactions as well as the resulting light and particle emissions is an essential step towards such achievements. This remains a considerable challenge, as the relevant scales typically range from picoseconds to attoseconds in time, and from micrometres to nanometres in space. In these experiments, owing to the extreme prevalent physical conditions, measurements can be performed only at macroscopic distances from the targets, yielding only partial information at these microscopic scales. This letter presents a major advance by applying the concepts of ptychography6, 7 to such measurements, and thus retrieving microscopic information hardly accessible until now. This paves the way to a general approach for the metrology of extreme laser–plasma interactions on very small spatial and temporal scales.

GIADA: shining a light on the monitoring of the comet dust production from the nucleus of 67P/Churyumov-Gerasimenko

During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta moni- tored the 67P coma dust environment for the entire period. Aims. We aim to describe the dust spatial distribution in the coma of comet 67P by means of in situ measurements. We determine dynamical and physical properties of cometary dust particles to support the study of the production process and dust environment modification. Methods. We analyzed GIADA data with respect to the observation geometry and heliocentric distance to describe the coma dust spatial distribu- tion of 67P, to monitor its activity, and to retrieve information on active areas present on its nucleus. We combined GIADA detection information with calibration activity to distinguish different types of particles that populate the coma of 67P: compact particles and fluffy porous aggregates. By means of particle dynamical parameters measured by GIADA, we studied the dust acceleration region. Results. GIADA was able to distinguish different types of particles populating the coma of 67P: compact particles and fluffy porous aggregates. Most of the compact particle detections occurred at latitudes and longitudes where the spacecraft was in view of the comet’s neck region of the nucleus, the so-called Hapi region. This resulted in an oscillation of the compact particle abundance with respect to the spacecraft position and a global increase as the comet moved from 3.36 to 2.43 AU heliocentric distance. The speed of these particles, having masses from 10−10 to 10−7 kg, ranged from 0.3 to 12.2 m s−1 . The variation of particle mass and speed distribution with respect to the distance from the nucleus gave indications of the dust acceleration region. The influence of solar radiation pressure on micron and submicron particles was studied. The integrated dust mass flux collected from the Sun direction, that is, particles reflected by solar radiation pressure, was three times higher than the flux coming directly from the comet nucleus. The awakening 67P comet shows a strong dust flux anisotropy, confirming what was suggested by on-ground dust coma observations performed in 2008.

Crystal structure of the RNA-dependent RNA polymerase from influenza C virus.

Negative-sense RNA viruses, such as influenza, encode large, multidomain RNA-dependent RNA polymerases that can both transcribe and replicate the viral RNA genome. In influenza virus, the polymerase (FluPol) is composed of three polypeptides: PB1, PB2 and PA/P3. PB1 houses the polymerase active site, whereas PB2 and PA/P3 contain, respectively, cap-binding and endonuclease domains required for transcription initiation by cap-snatching. Replication occurs through de novo initiation and involves a complementary RNA intermediate. Currently available structures of the influenza A and B virus polymerases include promoter RNA (the 5' and 3' termini of viral genome segments), showing FluPol in transcription pre-initiation states. Here we report the structure of apo-FluPol from an influenza C virus, solved by X-ray crystallography to 3.9 Å, revealing a new 'closed' conformation. The apo-FluPol forms a compact particle with PB1 at its centre, capped on one face by PB2 and clamped between the two globular domains of P3. Notably, this structure is radically different from those of promoter-bound FluPols. The endonuclease domain of P3 and the domains within the carboxy-terminal two-thirds of PB2 are completely rearranged. The cap-binding site is occluded by PB2, resulting in a conformation that is incompatible with transcription initiation. Thus, our structure captures FluPol in a closed, transcription pre-activation state. This reveals the conformation of newly made apo-FluPol in an infected cell, but may also apply to FluPol in the context of a non-transcribing ribonucleoprotein complex. Comparison of the apo-FluPol structure with those of promoter-bound FluPols allows us to propose a mechanism for FluPol activation. Our study demonstrates the remarkable flexibility of influenza virus RNA polymerase, and aids our understanding of the mechanisms controlling transcription and genome replication.

Effects of Dynamic High-Pressure Microfluidization Treatment and the Presence of Quercetagetin on the Physical, Structural, Thermal, and Morphological Characteristics of Zein Nanoparticles

The effects of dynamic high-pressure microfluidization (DHPM) and the addition of quercetagetin on the physical, structural, thermal, and morphological characteristics of zein nanoparticles were investigated. The result of Fourier transform infrared spectroscopy revealed that DHPM treatment caused the structural changes of zein, and the primary interactions between zein and quercetagetin were hydrogen bond and hydrophobic effects. Both of the DHPM treatment and the addition of quercetagetin resulted in the decrease of fluorescence intensity, the improved thermal stability, and the reducing of α-helix and the increase of β-sheets as proved by fluorescence spectra, differential scanning calorimetry thermograms, and circular dichroism spectra, respectively. It was found that the combined DHPM treatment and the addition of quercetagetin with mass ratio of zein to quercetagetin of 40:1 exhibited the morphology of nanospheres with more compact structure and uniform particle distribution.

A new compact solid-state neutral particle analyser at ASDEX Upgrade: Setup and physics modeling

At ASDEX Upgrade (AUG), a new compact solid-state detector has been installed to measure the energy spectrum of fast neutrals based on the principle described by Shinohara et al. [Rev. Sci. Instrum. 75, 3640 (2004)]. The diagnostic relies on the usual charge exchange of supra-thermal fast-ions with neutrals in the plasma. Therefore, the measured energy spectra directly correspond to those of confined fast-ions with a pitch angle defined by the line of sight of the detector. Experiments in AUG showed the good signal to noise characteristics of the detector. It is energy calibrated and can measure energies of 40-200 keV with count rates of up to 140 kcps. The detector has an active view on one of the heating beams. The heating beam increases the neutral density locally; thereby, information about the central fast-ion velocity distribution is obtained. The measured fluxes are modeled with a newly developed module for the 3D Monte Carlo code F90FIDASIM [Geiger et al., Plasma Phys. Controlled Fusion 53, 65010 (2011)]. The modeling allows to distinguish between the active (beam) and passive contributions to the signal. Thereby, the birth profile of the measured fast neutrals can be reconstructed. This model reproduces the measured energy spectra with good accuracy when the passive contribution is taken into account.

Effects of Initial Powder Compact Thickness, Lubrication, and Particle Morphology on the Cold Compaction Behavior of Ti Powder

This work investigates the compaction behavior of hydride–dehydride CP-Ti powder from green density/compaction pressure curves. These were obtained through a modification of selected processing conditions, such as variation in compact thickness, the use of internal lubrication, and additions of plasma rotating electrode process powder. A modified Cooper–Eaton equation, which treats the compaction process to be a combination of particle rearrangement (PR) and plastic deformation (PD) mechanisms, was used to simulate the curves. A comparison with aluminum and iron compaction is also carried out in this study. The research indicated that the cold compaction of titanium powder can be separated into two stages: a PR stage (stage I), which occurs at a compacting pressure in the range of 0 to 200 MPa, followed by a further PR stage initiated by PD, when the compaction pressure is in the range of 200 to 1000 MPa. The existence of stage II is due to the low plastic deformability of titanium and low density achieved at the end of stage I.

Dodecenylsuccinic Anhydride Pickering Emulsion Stabilized by Montmorillonite Nanoparticles Modified with Sodium Fluoride

Processing convenience and paper-sizing flexibility frequently require the delivery of alkenylsuccinic anhydride oil as emulsion. The shelf life of the oil is achieved kinetically, in most cases via the addition of surfactants such as cationic starch or a synthetic polymer, which are the subject of increasing scrutiny with regard to their environmental impact. The modification of montmorillonite nanoparticle with sodium fluoride was found to decrease the interfacial tension between dodecenylsuccinic anhydride (DDSA) and aqueous dispersion and to change the wettability of montmorillonite, which benefits the preparation of DDSA-in-water emulsions with enhanced stability, small droplet size, and improved hydrolysis resistance. Adjusting the pH and particle concentration of aqueous solution effectively improved the stability of DDSA emulsion. Catastrophic phase inversion from w/o (water-in-oil) to o/w (oil-in-water) was investigated by monitoring the variation of emulsion conductivity with increasing oil volume fraction. Evidence of the transition from loose particle-film to compact particle shell upon introduction of salt was found, as predicted theoretically for charged particles adsorbed on interfaces. Particulate interfacial films built by SFMMT nanoparticles protected DDSA droplets from aggregation and formed a honeycomb structure. Salt in the DDSA emulsification process restrained the hydrolytic action of DDSA effectively and sustained the sizing performance of DDSA even 5 h after the emulsion preparation.

Unusual temperature-induced swelling of ionizable poly(N-isopropylacrylamide)-based microgels: experimental and theoretical insights into its molecular origin.

In the traditional view of temperature-driven volume phase transitions in PNIPAM-based microgel solutions, a monotonic and sharp decrease in the particle size occurs upon heating the solution to above the volume phase transition temperature (VPTT). However, at sufficiently high microgel concentrations and under low salt conditions, our dynamic light scattering experiments reveal an unexpected non-monotonic evolution of the particle size when increasing the solution temperature. These findings show that poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) microgels swell upon heating the solution in the temperature range where NIPAM is water-soluble (i.e., below the VPPT). Further heating the microgel solution leads to microgel collapse as typically observed at temperatures above the VPTT. This novel behavior depends on the particle and salt concentration. We have observed the expected monotonic temperature-response of P(NIPAm-co-MAA) microgel solutions at low particle density and high salt concentration. To gain insights into the molecular origin of the unusual behavior of these microgel solutions, we have combined nuclear magnetic resonance studies and molecular-level theoretical calculations of the system. A delicate balance between inter-particle steric compressions and intra-microgel physical interactions and chemical equilibria determines the size of these microgels. Both steric compression, due to finite density, and hydrogen bond formation in the interior of the microgels favors a more compact particle. On the contrary, at the pH of the experiments the acid-base equilibrium constrains the polymer charge to increase, which favors particle swelling due to intra-microgel electrostatic repulsions. This interplay between physical interactions and chemical equilibria occurring at the nanometer length-scale determines the unusual thermal-induced swelling of P(NIPAM-co-MAA) microgels.

Scaling and design of high-energy laser plasma electron acceleration

Recently there has been great progress in laser-driven plasma-based accelerators by exploiting high-power lasers, where electron beams can be accelerated to multi-GeV energy in a centimeter-scale plasma due to the laser wakefield acceleration mechanism. While, to date, worldwide research on laser plasma accelerators has been focused on the creation of compact particle and radiation sources for basic sciences, medical and industrial applications, there is great interest in applications for high-energy physics and astrophysics, exploring unprecedented high-energy frontier phenomena. In this context, we present an overview of experimental achievements in laser plasma acceleration from the perspective of the production of GeV-level electron beams, and deduce the scaling formulas capable of predicting experimental results self-consistently, taking into account the propagation of a relativistic laser pulse through plasma and the accelerating field reduction due to beam loading. Finally, we present design examples for 10-GeV-level laser plasma acceleration, which is expected in near-term experiments by means of petawatt-class lasers.

Enhanced antisense oligonucleotide delivery using cationic liposomes incorporating fatty acid-modified polyethylenimine.

Antisense oligonucleotides (ASOs) have promising therapeutic potential in oncotherapy. However, low stability and efficacy limit their application in the clinic. Cationic liposomes have been investigated as delivery vehicles for ASOs. Here, we report the synthesis and evaluation of an ASO delivery vehicle comprising cationic liposomes incorporating fatty acid-modified polyethylenimine. An oleic acid derivative of branched polyethylenimine (PEI-OA) and a linoleic acid derivative of branched polyethylenimine (PEI-LA) were synthesized and incorporated into liposomes. The PEI-modified liposomes were synthesized by an ethanol injection method with composition of PEI-modified lipid/Chol/TPGS. The properties of these liposomes, including cytotoxicity, cellular uptake, ASO target silencing activity, based on mRNA and protein downregulation, were investigated. LOR-2501, an ASOs targeting ribonucleotide reductase R1 subunit (R1) was used as the therapeutic cargo. The PEI-modified liposomes showed relatively compact particle size and excellent colloidal stability for at least 25 days. PEI-modified liposomes effectively delivered LOR-2501 into KB cells and efficiently induced down-regulation of R1 mRNA and protein. Compared with regular cationic liposomes, PEI-modified liposomes was more effective, reducing R1 mRNA and protein by ~10%.

Development of a Novel Compact Particle Therapy Facility With Laser Driven Ion Beams via Gantry Systems Based on Pulsed Magnets

Development of a Novel Compact Particle Therapy Facility With Laser Driven Ion Beams via Gantry Systems Based on Pulsed Magnets

Friction and wear properties modification of Ti–6Al–4V alloy surfaces by implantation of multi-charged carbon ions

Carbon implantation into titanium is known to enhance some of its surface properties like wear behavior, mechanical hardness or the friction coefficient. Therefore the method is a candidate to be applied as a powerful surface engineering tool for titanium alloys. Recently, a new implantation technique has been developed, which is based on a compact particle accelerator device that is easy to handle. The device allows simultaneous multi-charged ion-implantation (from C+ up to C4+) in order to get a plateau like implantation profile based on the energetic distribution. The aim of this study is to investigate microstructural modifications of the near surface region of Ti–6Al–4V due to this processing technology and to enhance the surface performance. Nanoindentation and tribological measurements revealed a threshold of critical C contents where friction coefficient and wear are significantly reduced. Furthermore, these enhancements have been correlated to the presence of additional graphitic carbon.

Quasimonoenergetic collimated electron beams from a laser wakefield acceleration in low density pure nitrogen

A laser wakefield acceleration (LWFA) experiment is performed using 30 TW, 30 fs, and 800 nm laser pulses, focused onto pure nitrogen plasma having relatively low densities in the range of 0.8×1018 cm−3 to 2.7×1018 cm−3. Electron beams having a low divergence of ∼3 mrad (full-width at half-maximum) and quasi-monoenergetic peak energies of ∼105 MeV are achieved over 4-mm interaction length. The total electron beam charge reached to 2 nC, however, only 1%–2% of this (tens of pC) had energies >35 MeV. We tried different conditions to optimize the electron beam acceleration; our experiment verifies that lower nitrogen plasma densities are generating electron beams with high quality in terms of divergence, charge, pointing stability, and maximum energy. In addition, if LWFA is to be widely used as a basis for compact particle accelerators in the future, therefore, from the economic and safety points of view we propose the use of nitrogen gas rather than helium or hydrogen.

Design of a retarding potential grid system for a neutral particle analyzer.

The ion energy distribution in a magnetically confined plasma can be inferred from charge exchange neutral particles. On the Madison Symmetric Torus (MST), deuterium neutrals are measured by the Florida A&M University compact neutral particle analyzer (CNPA) and the advanced neutral particle analyzer (ANPA). The CNPA energy range covers the bulk deuterium ions to the beginning of the fast ion tail (0.34-5.2 keV) with high-energy resolution (25 channels) while the ANPA covers the vast majority of the fast ion tail distribution (∼10-45 keV) with low energy resolution (10 channels). Though the ANPA has provided insight into fast ion energization in MST plasma, more can be gained by increasing the energy resolution in that energy range. To utilize the energy resolution of the CNPA, fast ions can be retarded by an electric potential well, enabling their detection by the diagnostic. The ion energy distribution can be measured with arbitrary resolution by combining data from many similar MST discharges with different energy ranges on the CNPA, providing further insight into ion energization and fast ion dynamics on MST.

Capillary-driven percolating networks in ternary blends of immiscible polymers and silica particles

We investigate the structure and rheology of a melt-blended ternary system composed of a continuous polymer phase, silica particles in the few-micron size range, and a small amount of a second immiscible polymer phase which preferentially wets the particles. The morphology of the ternary system is found to consist of a volume-spanning “pendular network” of particles bridged by menisci of the wetting polymer, as well as “capillary aggregates” which are large compact particle aggregates saturated by the wetting polymer. The ternary blends have strongly non-Newtonian melt rheology due to the pendular network. The relative extent of capillary aggregation depends on the melt-blending history, and the rheological properties can be used to track the changes in the blend structure. The pendular network is seen at a particle loading of only 10 vol.%, demonstrating that capillary bridging lowers the percolation threshold of a particle-filled polymer.

Low energy ion distribution measurements in Madison Symmetric Torus plasmas

Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A&M University compact neutral particle analyzer (CNPA), used to measure the contents of neutral particle flux, has been reconfigured, calibrated, and installed on the Madison Symmetric Torus (MST) for high temperature deuterium plasmas. The energy range of the CNPA has been extended to cover 0.34–5.2 keV through an upgrade of the 25 detection channels. The CNPA has been used on all types of MST plasmas at a rate of 20 kHz throughout the entire discharge (∼70 ms). Plasma parameter scans show that the ion distribution is most dependent on the plasma current. Magnetic reconnection events throughout these scans produce stronger poloidal electric fields, stronger global magnetic modes, and larger changes in magnetic energy all of which heavily influence the non-Maxwellian part of the ion distribution (the fast ion tail).

Laser electron acceleration beyond 100 GeV

Nowadays there is great progress on laser-driven plasma-based accelerators by exploiting petawatt-class lasers, where for one aspect electron beams can be accelerated to multi-GeV energy in a centimeter-scale plasma due to laser wakefield acceleration mechanism. While to date, worldwide researches on laser-plasma accelerators are focused to create compact particle and radiation sources for applications in a wide range of sciences, including basic, medical and industrial sciences, there are great interests in applications for high energy physics and astrophysics that explore unprecedented high-energy frontier phenomena, for which laser plasma accelerator concepts provide us with promising tools. Here, our endeavors toward “extreme light” in the IZEST are envisaged for the next 30 years perspective and issues on laser plasma electron acceleration beyond 100 GeV and furthermore toward the TeV regime, aiming at high energy physics applications.

High-speed filtration using highly porous fiber media for advanced and compact particle removal

Since its recent introduction to the filtration industry, one of the major concerns about the use of fiber in water treatment has been its applicability for high-rate filtration while minimizing the build-up of headloss. In this study, a compact, modular filter employing non-woven, highly porous polypropylene fiber as filter media was investigated for the treatment of turbid water under high filtration rates. The impact of different operating variables such as polyaluminum chloride (PAC) dose and filtration rate on the effluent turbidity and headloss were investigated. Due to the fiber's high porosity, the filter was able to retain solids at a filtration rate of up to 1,500 m/day without headloss. When PAC was added, the effluent turbidity decreased significantly with the lowest observed when the dose was 1 mg/L. Furthermore, the effluent turbidity was found to increase with the filtration rate. During all the experiments, no headloss was observed except when the filtration rate was 2,250 m/day or when the PAC dose was 5 mg/L. In terms of its compactness and applicability at very high filtration rates, the polypropylene fiber filter can have a considerable advantage compared to other filters.

Thermal stability and folding kinetics analysis of disordered protein, securin

Lacking a stable tertiary structure, intrinsically disordered proteins (IDPs) possess particular functions in cell regulation, signaling, and controlling pathways. The study of their unique structural features, thermal stabilities, and folding kinetics is intriguing. In this study, an identified IDP, securin, was used as a model protein. By using a quasi-static five-step (on-path) folding process, the function of securin was restored and analyzed by isothermal titration calorimetry. Fluorescence spectroscopy and particle size analysis indicated that securin possessed a compact hydrophobic core and particle size. The glass transition of securin was characterized using differential scanning microcalorimetry. Furthermore, the folding/unfolding rates (kobs) of securin were undetectable, implying that the folding/unfolding rate is very fast and that the conformation of securin is sensitive to solvent environmental change. Therefore, securin may fold properly under specific physiological conditions. In summary, the thermal glass transition behavior and undetectable kobs of folding/unfolding reactions may be two of the indices of IDP.

An initial measurement of a fast neutral spectrum for ion cyclotron range of frequency heated plasma using two-channel compact neutral particle analyzers in KSTAR

The accurate measurement of fast neutral particles from high energy ion tails is very important since it is a measure of ion cyclotron range of frequency (ICRF) or neutral beam (NB) ion heating. In KSTAR, fast neutral measurements have been carried out using a compact neutral particle analyzer based on the silicon photo diode since 2010. As a result, the fast neutral spectrum was observed consistent with the ion temperature, diamagnetic energy, and neutron flux in 2011. However, there was fast neutral count beyond the injected neutral beam energy in NB-only heating. Since it is difficult to expect the count unless the temperature is high enough to diffuse the fast ions beyond the beam energy it was required to identify what it is. During the 2012 campaign, the two-channel diode detectors with and without a particle stopper were used to distinguish fast neutral counts and other counts by a hard X-ray or neutrons. As a result, it was confirmed that the high energy component beyond the beam energy originated from a hard X-ray or neutrons. Finally, it was observed that faster neutrals are generated by ICRF heating and enhanced by electron cyclotron heating compared to NB-only heating.