Artificial Particles Research Articles

Scattering signatures of suspended particles: an integrated system for combining digital holography and laser diffraction

The use of laser diffraction is now common practice for the determination of an in situ particle size distribution in the marine environment. However, various imaging techniques have shown that particles vary greatly in shape, leading to uncertainty in the response of laser diffraction instruments when subjected to this diverse range of complex particles. Here we present a novel integrated system which combines both digital in-line holography and a LISST-100 type C, to simultaneously record in-focus images of artificial and natural particles with their small-angle forward scattering signature. The system will allow for further development of a reliable alternative to Mie Theory when using laser diffraction for the in situ measurement of complex suspended particles. A more detailed knowledge of the performance of laser diffraction when subjected to the wide variety of complex particles found in the marine environment will then be possible.

3-D imaging and quantification of graupel porosity by synchrotron-based micro-tomography

Abstract. The air bubble structure is an important parameter to determine the radiation properties of graupel and hailstones. For 3-D imaging of this structure at micron resolution, a cryo-stage was developed. This stage was used at the tomography beamline of the Swiss Light Source (SLS) synchrotron facility. The cryo-stage setup provides for the first time 3-D-data on the individual pore morphology of ice particles down to infrared wavelength resolution. In the present study, both sub-mm size natural and artificial ice particles rimed in a wind tunnel were investigated. In the natural rimed ice particles, Y-shaped air-filled closed pores were found. When kept for half an hour at −8 °C, this morphology transformed into smaller and more rounded voids well known from literature. Therefore, these round structures seem to represent an artificial rather than in situ pore structure, in contrast to the observed y-shaped structures found in the natural ice particles. Hence, for morphological studies on natural ice samples, special care must be taken to minimize any thermal cycling between sampling and measurement, with least artifact production at liquid nitrogen temperatures.

Characteristics of Artificial Virus-like Particles Assembled in vitro from Potato Virus X Coat Protein and Foreign Viral RNAs

Potato virus X (PVX) and some other potexviruses can be reconstitutedin vitrofrom viral coat protein (CP) and RNA. PVX CP is capable of forming viral ribonucleoprotein complexes (vRNP) not only with homologous, but also with foreign RNAs. This paper presents the structure and properties of vRNP assembledin vitroupon incubation of PVX CP and RNAs of various plant and animal viruses belonging to different taxonomic groups. We have shown that the morphology and translational properties of vRNPs containing foreign (heterologous) RNA are identical to those of homological vRNP (PVX RNA - PVX CP). Our data suggest that the assembly of the "mixed" vRNPin vitrocould be started at the 5'-proximal region of the RNA, producing a helical structure of vRNPs with foreign nucleic acids. The formation of heterologous vRNPin vitrowith PVX CP appears not to require a specific 5' end RNA nucleotide sequence, and the PVX CP seems to be able to pack foreign genetic material of various sizes and compositions into artificial virus-like particles.

Comparative study of structure and properties of nucleoproteides synthesized using plant virus coat protein

The self-assembly of virus-like artificial particles from the coat protein of a helical virus (potato virus X) and nucleic acids (RNA and DNA) is studied. The structure and properties of the particles are investigated by transmission electron microscopy, atomic force microscopy, and enzymatic analysis.

An experimental study of Hapke’s modeling of natural granular surface samples

A series of natural granular surfaces composed of volcanic samples that widely vary in grain sizes (from the micron-scale to the millimeter-scale), shapes, surface aspects, origins, and including glass and minerals, has been measured in the visible domain with the spectro-imaging device ISEP (Observatoire Midi-Pyrénées, Toulouse, France) and inverted by photometric modeling. The experimental protocol makes use of a specific set of multiangular configurations (on the order of a few tens) with sufficient angular diversity and coverage of the bidirectional space to resolve differences in particle phase function behavior and surface texture. This restrained set delivers comparable results in terms of photometric parameters to those produced with a dense set of hundreds of measurements. The considered samples in this work have been chosen to assess the influence of varied physical properties on light scattering behavior. The following specific photometric trends are found. Samples comprising fresh glass or monocrystals in a proportion on the order of 30% or more (from binocular magnifying glass inspection) are extremely forward scattering with narrow scattering lobes, and the larger the particles, the narrower the scattering lobe; also, round particles tend to be more backscattering than irregularly-shaped ones of similar texture, and the presence of voids within particles tends to increase the backscattering character of the sample. Particles with broad scattering lobes (phase function asymmetry parameter b ⩽ 0.5) display relatively large modeled surface macroscopic roughness values (15–25°), while particles with narrow scattering lobes ( b ⩾ 0.5) show smaller modeled surface macroscopic roughness (between 15° and ∼3°). The comparison between the present results for the scattering parameters b and c, and those obtained in previous studies from artificial particles shows a similar trend and general agreement although some discrepancies were observed. The granular surface samples analyzed in the present study that contain a high proportion of isolated translucent monocrystals and/or fresh glass appear extremely forward-scattering and clearly chart a new part of the c vs. b trend. This is further supported by recent similar findings for martian in situ data and lunar regolith simulants. These results should help to better interpret present and future orbital and landed photometric data from bodies’ surfaces such as the Moon’s, Mars’, Vesta’s or Mercury’s regolith.

Characterization of the pattern of ischemic stroke induced by artificial particle embolization in the rat brain

Embolism is responsible for half of cerebral infarctions, yet few animal models were developed due to the unpredictability of the embolus-induced infarcts. We manufactured artificial embolic particles by blending chitin and poly(d,l-Lactide-co-glycolide) (chitin/PLGA) for their good biocompatibility and rapid hydration expansion property. We subdivided the chitin/PLGA microparticles into 10 size groups (from 38–45 μm to 255–350 μm) and injected them through the external carotid artery toward the bifurcation of the common carotid artery in the rat. Reduced blood flow of the ipsilateral hemisphere was evident immediately after the injection of particles. The spherical appearance of the particle was critical in occluding the cerebral vessels. Particle212–250μm produced the greatest diffuse infarction in the ipsilateral hemisphere, including the cortex, hippocampus, basal ganglion, thalamus, midbrain and cerebellum. Particle75-90μm induced single or sparse isolated infarcts mainly located in the subcortical region, resembling lacunar stroke observed in humans. Particle38–45μm frequently crossed to the contralateral hemisphere and induced diffuse infarctions in both hemispheres. The cortex infarct volumes were positively correlated to neurologic score and seizure incidence. In conclusion, we have established embolic stroke animal models, including a novel model that mainly expresses lacunar infarction, by intravenous injection of chitin/PLGA microparticles.

Synthetic Protocells Interact with Viral Nanomachinery and Inactivate Pathogenic Human Virus

We present a new antiviral strategy and research tool that could be applied to a wide range of enveloped viruses that infect human beings via membrane fusion. We test this strategy on two emerging zoonotic henipaviruses that cause fatal encephalitis in humans, Nipah (NiV) and Hendra (HeV) viruses. In the new approach, artificial cell-like particles (protocells) presenting membrane receptors in a biomimetic manner were developed and found to attract and inactivate henipavirus envelope glycoprotein pseudovirus particles, preventing infection. The protocells do not accumulate virus during the inactivation process. The use of protocells that interact with, but do not accumulate, viruses may provide significant advantages over current antiviral drugs, and this general approach may have wide potential for antiviral development.

Investigating Arsenic Bioavailability and Bioaccumulation by the Freshwater Oligochaete Lumbriculus variegatus

The complex and variable composition of natural sediments makes it difficult to predict the bioavailability and bioaccumulation of sediment-bound contaminants. Several approaches, including an experimental model using artificial particles as analogues for natural sediments, have been proposed to overcome this problem. For this work, we applied this experimental device to investigate the uptake and bioaccumulation of As(III) by the freshwater oligochaete Lumbriculus variegatus. Five different particle systems were selected, and particle-water partition coefficients for As(III) were calculated. The influence of different concentrations of commercial humic acids was also investigated, but this material had no effect on bioaccumulation. In the presence of particulate matter, the bioaccumulation of As(III) by the oligochaetes did not depend solely on the levels of chemical dissolved but also on the amount sorbed onto the particles and the strength of that binding. This study confirms that the use of artificial particles may be a suitable experimental model for understanding the possible interactions that may occur between contaminants and particulate matter. In addition, it was found that the most hydrophobic resin induced an increase in arsenic bioavailability, leading to the highest bioaccumulation to L. variegatus compared with animals that were exposed to water only.

Using artificial fluorescent particles as tracers of livestock wastes within an agricultural catchment

Evidence for the movement of agricultural slurry and associated pollutants into surface waters is often anecdotal, particularly with relation to its ‘particulate’ components which receive less attention than ‘bio-available’ soluble phases. To assess the extent of movement of slurry particles artificial fluorescent particles were mixed with slurry and applied to a field sub-catchment within a headwater catchment. Particles were 2–60 μm in diameter and two different densities, 2.7 and 1.2 g cm –3 representing ‘inorganic’ and ‘organic’ material. Water samples from the field and catchment outlet were collected during two storm events following slurry application and analysed for particle and suspended sediment concentrations (SSC). SSC from the field and catchment outlet always formed clockwise hysteresis loops indicating sediment exhaustion and particles of the two densities were always found to be positively correlated. Particles from the field formed clockwise hysteresis loops during the first discharge event after slurry application, but anti-clockwise hysteresis loops during the second monitored event which indicated a depletion of readily mobilisable particles. Particles from the catchment outlet always formed anticlockwise hysteresis loops. Particle size became finer spatially, between field and catchment outlet, and temporally, between successive storm events. The results indicate that slurry particles may be readily transported within catchments but that different areas may contribute to pollutant loads long after the main peak in SSC has passed. The density of the particles did not appear to have any effect on particle transport however the size of the particles may play a more important role in the 2–60 μm range.

Geological variation in particle surface-roughness preference in the case-bearing caddisflies

Optimality modeling suggests that the choice of resources often represents the best achievable balance of costs and benefits. However, there is no empirical data describing the effect of resource availability on the development of the material choice behavior during construction of a biological structure. Cylindrical case-bearing caddisfly larvae prefer smooth-surface particles to allow construction of a smooth interior case wall. We evaluated the relationship between case material preference and the local availability of sand particle species in 7 distant populations of 2 odontocerid species, Psilotreta kisoensis and Perissoneura paradoxa. The field survey revealed that all populations selectively used the smooth particles from the surrounding sediment to construct their cases. However, when comparing among populations, the larvae originating from areas with relatively few smooth particles constructed cases using rougher particles. We then forced the larvae to choose from a mixture of equal amounts of 2 artificial particles that had different textures (rough and smooth). The preference for smooth artificial particles was lower in populations that naturally incorporated rougher particles in their cases. Our results are consistent with the predictions of optimal foraging theory as the populations living in areas with abundant smooth particles had a stronger preference for smoothness than those in areas where such particles were rare. The abundance of smooth particles in the sediment depended on its mineralogical/ petrological origin. Thus, we suggest that material preference is influenced by local geology. Our results provide important insight into the mechanisms controlling construction behavior. Key words: construction behavior, decision making, optimality theory, sediment geology, surface roughness, Trichoptera. [Behav Ecol]

Nanobiotechnology and blood substitutes

Sir, Nanobiotechnology is the assembling of biological molecules into 1–100 nm dimensions. These dimensions can be the diameter of nanodimension artificial cells or particles; membranes with nanodimension thickness or nanotubules with nanodimension diameter.[1] Since red blood cell (RBC) membrane includes blood group antigens, typing and matching are required earlier than they can be transfused into patients; these result in delays in emergency situations. The storage time using regular method is merely about 42 days. RBCs cannot be sterilized to remove infective agents like hepatitis viruses, HIV, and other probable emerging infective agents. Thus, RBCs substitutes are being developed. RBC contains hemoglobin (Hb), antioxidant enzymes, and multienzyme system to prevent the conversion of Hb into nonfunctioning met Hb. It has been shown as far back as 1957 that artificial RBC can be prepared with ultrathin polymer membranes of nanodimension thickness. To increase the circulation time, the first-generation engineered Hb is formed by using glutaraldehyde to crosslink Hb into soluble nanodimension polyhemoglobin (poly-Hb) that has been tested clinically in patients. Further extension includes conjugated Hb, intramolecularly crosslinked Hb, and recombinant Hb. For certain clinical uses, in addition to engineered Hb, antioxidants need to remove oxygen radicals to prevent injury from ischemia reperfusion. Nanobiotechnology is used to prepare second-generation engineered Hb by assembling Hb together with superoxide dismutase (SOD) and catalase (CAT) to form a nanodimension soluble complex of poly-Hb-CAT-SOD. A third-generation system is to prepare nanodimension complete artificial RBCs that can circulate for sufficient length of time after infusion. One approach uses lipid vesicles to encapsulate Hb. Another approach to use biodegradable polymer-like polylactic acid or a copolymer of polyethylene glycol–polylactide (PEG-PLA) to form the membrane of nanodimension completes artificial RBC.[2] Past experience has shown that it takes many years to develop ideas on blood substitutes into products and that lack of basic information has resulted in much failure and delays. It is important to carry out basic research to gain important basic information needed for the simultaneous development of blood substitutes. In the meantime, two types of first-generation nanodimension poly-Hb are in the final stages of clinical trials in human and one of these has been approved for routine clinical uses in patients in South Africa. New nanodimension-conjugated Hb is also being tested in clinical trial. Shortage of human Hb is being resolved by studies on recombinant human Hb, placenta Hb, bovine Hb, and synthetic heme. Meanwhile, new generations of modified Hb are being developed that can modulate the effects of nitric oxide for those clinical applications that might have potential problems related to oxygen radicals. Poly-Hb can be crosslinked to an enzyme to suppress the growth of tumor. A further development is the use of PEG-lipids or PEG-biodegradable polymer membranes to prepare nanodimension artificial RBCs containing Hb and complex enzyme systems. Many other extensions and modifications of this general principle of blood transfusion in nanobiotechnology are possible.

Bacterial Magnetosome: A Novel Biogenetic Magnetic Targeted Drug Carrier with Potential Multifunctions

Bacterial magnetosomes (BMs) synthesized by magnetotactic bacteria have recently drawn great interest due to their unique features. BMs are used experimentally as carriers for antibodies, enzymes, ligands, nucleic acids, and chemotherapeutic drugs. In addition to the common attractive properties of magnetic carriers, BMs also show superiority as targeting nanoscale drug carriers, which is hardly matched by artificial magnetic particles. We are presenting the potential applications of BMs as drug carriers by introducing the drug-loading methods and strategies and the recent research progress of BMs which has contributed to the application of BMs as drug carriers.

Morphological characterization of soot aerosol particles during LACIS Experiment in November (LExNo)

Combined mobility and aerodynamic measurements were used to characterize the morphology of soot particles in an experimental campaign on the hygroscopic growth and activation of an artificial biomass burning aerosol. A custom‐made, single‐stage low‐pressure impactor and two aerosol mass spectrometers (AMS) operating in the free molecular regime were used to measure the vacuum aerodynamic diameter of mobility‐selected artificial soot particles that were produced in a spark discharge generator and then modified by condensation of ammonium hydrogen sulfate or levoglucosan as a coating to change their hydroscopic activity. Transmission electron microscope images revealed a relationship between the electrical mobility diameter and the diameter of the enveloping sphere, thus enabling evaluation of the effective density of soot agglomerates. A fractal description of the morphology of the soot aggregates allowed for evaluation of the average mass of the hygroscopic material per particle. The average mass of the hygroscopic material per particle was also measured directly with the two AMS instruments, and the agreement between the two methods was found satisfactory. This tandem approach allows detection of small changes in the particle effective density and morphology caused by condensation of organic material.

The organic fraction of bubble-generated, accumulation mode Sea Spray Aerosol (SSA)

Abstract. Recent studies have detected a dominant accumulation mode (~100 nm) in the Sea Spray Aerosol (SSA) number distribution. There is evidence to suggest that particles in this mode are composed primarily of organics. To investigate this hypothesis we conducted experiments on NaCl, artificial SSA and natural SSA particles with a Volatility-Hygroscopicity-Tandem-Differential-Mobility-Analyser (VH-TDMA). NaCl particles were atomiser generated and a bubble generator was constructed to produce artificial and natural SSA particles. Natural seawater samples for use in the bubble generator were collected from biologically active, terrestrially-affected coastal water in Moreton Bay, Australia. Differences in the VH-TDMA-measured volatility curves of artificial and natural SSA particles were used to investigate and quantify the organic fraction of natural SSA particles. Hygroscopic Growth Factor (HGF) data, also obtained by the VH-TDMA, were used to confirm the conclusions drawn from the volatility data. Both datasets indicated that the organic fraction of our natural SSA particles evaporated in the VH-TDMA over the temperature range 170–200 °C. The organic volume fraction for 71–77 nm natural SSA particles was 8±6%. Organic volume fraction did not vary significantly with varying water residence time (40 s to 24 h) in the bubble generator or SSA particle diameter in the range 38–173 nm. At room temperature we measured shape- and Kelvin-corrected HGF at 90% RH of 2.46±0.02 for NaCl, 2.35±0.02 for artifical SSA and 2.26±0.02 for natural SSA particles. Overall, these results suggest that the natural accumulation mode SSA particles produced in these experiments contained only a minor organic fraction, which had little effect on hygroscopic growth. Our measurement of 8±6% is an order of magnitude below two previous measurements of the organic fraction in SSA particles of comparable sizes. We stress that our results were obtained using coastal seawater and they can't necessarily be applied on a regional or global ocean scale. Nevertheless, considering the order of magnitude discrepancy between this and previous studies, further research with independent measurement techniques and a variety of different seawaters is required to better quantify how much organic material is present in accumulation mode SSA.

Assessing multiple novel tracers to improve the understanding of the contribution of agricultural farm waste to diffuse water pollution

A study was undertaken on drained and undrained 1 ha grassland lysimeters to assess the effectiveness of multiple novel tracing techniques in understanding how agricultural slurry waste moves from land to water. Artificial fluorescent particles designed to mimic the size and density of organic slurry particles were found to move off the grassland via inter-flow (surface + lateral through-flow) and drain-flow. Where both pathways were present the drains carried the greater number of particles. The results of the natural fluorescence and δ13C of water samples were inconclusive. Natural fluorescence was higher from slurry-amended lysimeters than from zero-slurry lysimeters, however, a fluorescence decay experiment suggested that no slurry signal should be present given the time between slurry application and the onset of drainage. The δ13C values of >0.7 microm and <0.7 microm material in drainage were varied and unrelated to discharge. The mean value of >0.7 microm δ13C in water from the drain-flow pathways was higher from the lysimeter which had received naturally enriched maize slurry compared to the lysimeter which received grass slurry indicating a contribution of slurry-derived material. Values of <0.7 microm δ13C from the same pathway, however, produced counter intuitive trends and may indicate that different fractions of the slurry have different δ13C values.

Interpretation of Wild 2 dust fine structure: Comparison of Stardust aluminum foil craters to the three‐dimensional shape of experimental impacts by artificial aggregate particles and meteorite powders

Abstract— New experimental results show that Stardust crater morphology is consistent with interpretation of many larger Wild 2 dust grains being aggregates, albeit most of low porosity and therefore relatively high density. The majority of large Stardust grains (i.e. those carrying most of the cometary dust mass) probably had density of 2.4 g cm−3 (similar to soda‐lime glass used in earlier calibration experiments) or greater, and porosity of 25% or less, akin to consolidated carbonaceous chondrite meteorites, and much lower than the 80% suggested for fractal dust aggregates. Although better size calibration is required for interpretation of the very smallest impacting grains, we suggest that aggregates could have dense components dominated by μm‐scale and smaller sub‐grains. If porosity of the Wild 2 nucleus is high, with similar bulk density to other comets, much of the pore space may be at a scale of tens of micrometers, between coarser, denser grains.Successful demonstration of aggregate projectile impacts in the laboratory now opens the possibility of experiments to further constrain the conditions for creation of bulbous (Type C) tracks in aerogel, which we have observed in recent shots. We are also using mixed mineral aggregates to document differential survival of pristine composition and crystalline structure in diverse finegrained components of aggregate cometary dust analogues, impacted onto both foil and aerogel under Stardust encounter conditions.

Assessing the importance of dietborne cadmium and particle characteristics on bioavailability and bioaccumulation in the nematodeCaenorhabditis elegans

To investigate the impact of multiple cadmium exposure pathways on bioavailability and bioaccumulation, Caenorhabditis elegans were exposed to either dissolved cadmium or to both particulate (dietborne) and dissolved cadmium. The dietborne metal exposure scenarios included evaluations of two bacteria species (Escherichia coli and Arthrobacter globiformis), varying bacteria concentrations, artificial particles (with different surface functional groups or coated with lipopolysaccharides), as well as a mixture of both bacteria and artificial particles. Total cadmium concentration in the nematodes was used as a proxy for total metal accumulation. Internal cadmium availability was determined using the cadmium-responsive gene-1 (cdr-1) transcript level, as quantified by real-time polymerase chain reaction. Particle-associated exposure was the predominant contributor to cadmium bioavailability and bioaccumulation; however, no clear relationship between cdr-1 expression and cadmium body burden was observed. The quality and quantity of particles, rather than the total particle-associated metal load, was of primary importance in regulating cadmium uptake and accumulation. Nematodes exposed to cadmium-contaminated bacteria displayed significantly higher levels of cdr-1 expression relative to artificial particles. Furthermore, C. elegans displayed a statistically significant difference in cadmium accumulation patterns between the biotic diet, abiotic particles, and aqueous phase. Waterborne exposure caused an increase in total cadmium body burden following inhibition of the P-glycoprotein transport system in nematodes. This may suggest that cadmium taken up by the aqueous phase is detoxified preferentially by excretion.

Simulation of rocket seeding of convective clouds with coarse-dispersion hygroscopic aerosol. 2. Condensation and coagulation in a cloud seeded with hygroscopic particles

A set of equations is developed to describe changes in cloud dispersity due to condensation and gravitational coagulation in the area of the salt particle diffusion in hygroscopic seeding of convective clouds with antihail rockets. Competition for moisture between the natural cloud droplets, entrained in the area from outside by turbulent diffusion, and artificial NaCl particles is taken into account. Optimum versions of hygroscopic seeding aimed at precipitation enhancement are discussed.

Inter-Comparison of a Fast Mobility Particle Sizer and a Scanning Mobility Particle Sizer Incorporating an Ultrafine Water-Based Condensation Particle Counter

An Ultrafine Water-based Condensation Particle Counter (UWCPC), a Scanning Mobility Particle Sizer (SMPS) incorporating an UWCPC, and a Fast Mobility Particle Sizer (FMPS) were deployed to determine the number and size distribution of ultrafine particles. Comparisons of particle number concentrations measured by the UWCPC, SMPS, and FMPS were conducted to evaluate the performance of the two particle sizers using ambient particles as well as lab generated artificial particles. The SMPS number concentration was substantially lower than the FMPS (FMPS/SMPS = 1.56) measurements mainly due to the diffusion losses of particles in the SMPS. The diffusion loss corrected SMPS (C-SMPS) number concentration was on average ∼ 15% higher than the FMPS data (FMPS/C-SMPS = 0.87). Good correlation between the C-SMPS and FMPS was also observed for the total particle number concentrations in the size range 6 nm to 100 nm measured at a road-side urban site (r2 = 0.91). However, the particle size distribution measured by the ...

WIND TUNNEL STUDY ON THE EFFECT OF ROOF WIND PRESSURE OF BUILDINGS ON SHAPING ROOF SNOW ACCUMULATIONS

In estimating the unbalanced snow loads on roofs of buildings in cold and heavy snow regions, it is important to consider the aerodynamic influence of buildings on shaping snow accumulations. At present, the information from snowstorm wind tunnel tests are effective to predict the typical snow accumulation patterns on various roof shapes. On the other hand, it will be useful if it is possible to estimate the snow accumulation patterns from simple characteristics of the wind flow around a building. This study focuses the relationship between the snow accumulation from snowstorm wind tunnel tests using artificial snow particles and the distribution of the mean wind pressure coefficients on roofs from the general wind tunnel tests. As a result of investigating five types of roofs such as a flat roof, a flat roof with parapet, a two-level flat roof, a hemisphere dome and a gable roof for a single snowstorm, it is found that the formation of the snow accumulation on roofs strongly depends on the gradient of the mean wind pressure coefficients on roofs.