Few Tens Of Particles Research Articles

Simple and Broadly Applicable Definition of Shear Transformation Zones.

Plastic deformation in amorphous solids is known to be carried by stress-induced localized rearrangements of a few tens of particles, accompanied by the conversion of elastic energy to heat. Despite their central role in determining how glasses yield and break, the search for a simple and generally applicable definition of the precursors of those plastic rearrangements-the so-called shear transformation zones (STZs)-is still ongoing. Here we present a simple definition of STZs-based solely on the harmonic approximation of a glass's energy. We explain why and demonstrate directly that our proposed definition of plasticity carriers in amorphous solids is more broadly applicable compared to anharmonic definitions put forward previously. Finally, we offer an open-source library that analyzes low-lying STZs in computer glasses and in laboratory materials such as dense colloidal suspensions for which the harmonic approximation is accessible. Our results constitute a physically motivated methodological advancement towards characterizing mechanical disorder in glasses, and understanding how they yield.

Characterizing the phase diagram of finite-size dipolar Bose-Hubbard systems

We use state-of-the-art density matrix renormalization group calculations in the canonical ensemble to determine the phase diagram of the dipolar Bose-Hubbard model on a finite cylinder. We consider several observables that are accessible in typical optical lattice setups and assess how well these quantities perform as order parameters. We find that, especially for small systems, the occupation imbalance is less susceptible to boundary effects than the structure factor in uncovering the presence of a periodic density modulation. By analysing the non-local correlations, we find that the appearance of supersolid order is very sensitive to boundary effects, which may render it difficult to observe in quantum gas lattice experiments with a few tens of particles. Finally, we show how density measurements readily obtainable on a quantum gas microscope allow distinguishing between superfluid and solid phases using unsupervised machine-learning techniques.

Efficient Device-Independent Entanglement Detection for Multipartite Systems

Entanglement is one of the most studied properties of quantum mechanics for its application in quantum information protocols. Nevertheless, detecting the presence of entanglement in large multipartite sates continues to be a great challenge both from the theoretical and the experimental point of view. Most of the known methods either have computational costs that scale inefficiently with the number of particles or require more information on the state than what is attainable in everyday experiments. We introduce a new technique for entanglement detection that provides several important advantages in these respects. First, it scales efficiently with the number of particles, thus allowing for application to systems composed by up to few tens of particles. Second, it needs only the knowledge of a subset of all possible measurements on the state, therefore being apt for experimental implementation. Moreover, since it is based on the detection of nonlocality, our method is device independent. We report several examples of its implementation for well-known multipartite states, showing that the introduced technique has a promising range of applications.

Origin and impact of particle-to-particle variations in composition measurements with the nano-aerosol mass spectrometer

In the nano-aerosol mass spectrometer, individual particles in the 10-30 nm size range are trapped and irradiated with a high pulse energy laser beam. The laser pulse generates a plasma that disintegrates the particle into atomic ions, from which the elemental composition is determined. Particle-to-particle variations among the mass spectra are shown to arise from plasma energetics: Low ionization energy species are enhanced in some spectra while high ionization energy species are enhanced in others. These variations also limit the accuracy and precision of elemental analysis, with higher deviations generally observed when low ionization energy species are dominant in the mass spectrum. For standard datasets generated from nominally identical particles, it is shown that that the error associated with composition measurement is random and that averaging the spectra from a few tens of particles is sufficient for measuring the mole fractions of common elements to within about 10% of the expected value. Averaging a greater number of particles offers limited improvement of the measurement precision but has the deleterious effect of degrading the measurement time-resolution, which is given by the time needed to obtain the required number of particle spectra for averaging. An internally mixed ambient particle dataset was found to give a similar result to the standard datasets, that is, the measured elemental composition converged to the average value after a few tens of particles were averaged.

Indirect estimation of the solar wind conditions in 29–31 October 2003

A comparative analysis of the solar wind conditions was performed for extremely disturbed event on 29–31 October 2003. It was found that the ACE and Geotail upstream monitors provided very similar data on the IMF but that plasma measurements in the SOHO CELIAS/MTOF, ACE SWEPAM, IMP 8 MIT, and Geotail CPI experiments are very different. The solar wind velocity was indirectly estimated using the time lag for propagation of such solar wind structures as interplanetary shock, Alfven waves, rotational, and tangential discontinuities from point L1 to the Earth. We found the best correspondence of the estimated velocity was with the ACE SWEPAM data, which displayed very fast (up to 2000 km/s) solar wind, while the IMP 8, Geotail, and SOHO plasma instruments are unable to measure such a fast solar wind stream. Application of the magnetopause models to a data set of numerous geosynchronous magnetopause crossings observed by GOES and LANL satellites enabled estimation of the solar wind dynamic pressure. In general the estimated pressure and density are in agreement with the solar wind plasma parameters provided by the ACE SWEPAM experiment. An estimation of the solar wind density corresponds very well to the electron density restored from the Geotail PWI data. However, during 1600–1800 UT on 29 October, 1700–1800 UT on 30 October, and 0000–0400 UT on 31 October, the estimated solar wind pressure and density are several times larger than provided by the Geotail PWI and ACE SWEPAM. A large helium abundance is considered as a possible reason for the solar wind pressure underestimation in the first case. The understated solar wind density on 30–31 October might be explained by errors in the method for restoring of the plasma data in fast solar wind (>900 km/s) accompanied with intensive fluxes (few tens of particles per cm2 s sr) of high‐energy (>30 MeV) solar energetic protons.

Ceilometer observations of aerosol layer structure above the Petit Lubéron during ESCOMPTE's IOP 2

A modified ceilometer has been used during the second Intensive Observation Period (IOP) of the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transport d'Émission” (ESCOMPTE) to perform continuous remote observations of aerosol accumulations in the first 3 km of the atmosphere. These observations encompassed an episode of intense particulate and photochemical pollution. The submicronic particles density, measured at an altitude of 600 m, went from a very low point of a few tens of particles per cubic centimeter (at the end of a Mistral episode in the free atmosphere) to a high point of more than 4500 particles per cubic centimeter (when pollutants were trapped by thermal inversions). The main result is that this instrument enables a fine documentation of the mixing layer height and of aerosol particles stratifications and circulation. Airborne aerosol measurements have been made above the mountainous region of Mérindol in order to validate in situ the remote sensing measurements. Ozone measurements near the summit of the mountains as well as in the valley were performed in order to correlate aerosol accumulation and ozone concentration. As a notable example, the two-layer aerosol stratification seen in the first 2 days of IOP 2b in that part of the ESCOMPTE domain confirms the results of another team which used backtrajectories. The low-altitude pollution for this timeframe had a local origin (the Fos industrial area), whereas above 500 m, the air masses had undergone regional-scale transport (from north-eastern Spain). The second major result is the highlighting of a pattern, in sea breeze conditions and in this part of the ESCOMPTE experiment zone, of nocturnal aerosol accumulation at an altitude of between 500 and 2000 m, followed by high ozone concentration the next day.

Airborne measurements of aerosol extinction in the lower and middle troposphere over Wyoming, USA

Particle size distributions, and scattering and absorption coefficients were measured over the Green River basin of Wyoming during the Southwest Wyoming Visibility Study (SWYVIS) in February and March 1996. Eleven flights were carried out, using the Wyoming King Air research aircraft. In the least polluted regions of the planetary boundary layer, particle number densities detected in the diameter range 0.13–3.0 μm were <100 cm −3. Aloft, in the stable air of the free troposphere, they were generally even lower, often falling to a few tens of particles per cm 3. Analyses of bulk aerosol filter samples showed that organic carbonaceous material was the dominant chemical component, with sulfate and refractory species being the largest inorganic components. Combining the filter data with separately measured black carbon mass loading values allowed refractive indices for the aerosol to be calculated, so that PCASP measured size distributions could be revised. Characterizing size parameters were obtained by fitting particle populations to bimodal lognormal distributions. Particle size distributions were somewhat broader at higher altitudes so that larger particles made greater contributions to extinction. Optical closure was attempted by comparing scattering and total extinctions computed by Mie theory with the corresponding values derived from the observations. While the calculated and measured single scattering albedo average values were in reasonably good agreement, even though individual pairs of values sometimes differed significantly, computed scattering coefficients often exceeded those derived from the measurements, by an average of 60%. Reasons for this discrepancy are explored, including the possible modification of the size distribution by partial or total volatilization of particles within the nephelometer and its inlet.

Study of RPC gas mixtures for the ARGO-YBJ experiment

The ARGO-YBJ experiment consists of a Resistive Plate Counter (RPC) carpet to be operated at the Yangbajing laboratory (Tibet, China), 4300 m a.s.l., and devoted to the detection of showers initiated by photon primaries in the energy range 100 GeV–20 TeV. The measurement technique, namely the timing on the shower front with a few tens of particles, requires RPC operation with 1 ns time resolution, low strip multiplicity, high efficiency and low single counting rate. We have tested RPCs with many gas mixtures, at sea level, in order to optimize these parameters. The results of this study are reported here.

PHASE TRANSITION AND FRAGMENT PRODUCTION IN THE LATTICE GAS MODEL

The critical behavior of fragment production is studied within a Lattice Gas Model in the canonical ensemble. Finite size effects on the liquid-gas phase transition are analyzed by a direct calculation of the partition function, and it is shown that phase coexistence and phase transition are relevant concepts even for systems of a few tens of particles. Critical exponents are extracted from the behavior of the fragment production yield as a function of temperature by means of a finite size scaling. The result is that in a finite system well defined critical signals can be found at supercritical (Kertész line) as well as subcritical densities inside the coexistence zone.

Interaction of solar flare X-rays with the atmosphere of Titan

During solar flares an intense flux of X-rays is emitted into space. When it reaches Saturns orbit, it is still strong enough to significantly disturb Titans dense atmosphere. The main effect is to ionize the neutral component of the atmosphere and to increase, therefore, the electron and ion density at altitudes of 400–900 km. Especially near a maximum of the solar cycle, when flare activity is high, the average plasma density can, for long intervals, remain at a level of a few tens of particles per cm 3. As a result, the atmospheric photochemistry will be affected, but also an increase of production rate of small haze particles might be expected. Ionized atoms are usually excited ; when they relax to the ground level in the process of resonant fluorescence, Titans albedo at specific wavelengths increases. It is estimated that at Earth orbit the flux of photons emitted from Titan in the 3 KeV argon line during a strong X1-type flare is equal to 1.6×10 −20 J m −2 s −1 for 10% Ar abundance in Titans atmosphere.

The stability of superspheres

The stability of superspheres containing a few tens of particles, formed by the aggregation of weakly charged spherical colloidal crystalites, can be explained by the existence of two opposing forces of different range within the superspheres: long-range electrostatic repulsion and shortrange attractive dispersion. A condition of stability is found that is in quantitative agreement with observation. The superspheres are a manifestation of frustration, analogous to frustration in spin glasses. The generality of the phenomenon is discussed.

Concentration and size variation of condensation nuclei at Mawson, Antarctica

Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm-3 in summer and a minimum of a few tens of particles per cm-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 μm in winter to around 0.04 μm in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.