Small Size End Research Articles

Side Milling of Helical End Mill Oscillated in Axial Direction with Ultrasonic Vibration

This paper is focused on the cutting performance in the side milling of a small-size end mill with vibrations generated by an ultrasonic vibration spindle apparatus in the axial direction with a helix edge. In side milling with ultrasonic vibration in the rotational direction, the mean value of the cross-sectional chip area per cutting time decreases owing to the frequent repetition of the cutting and non-cutting phases. As a result, the cutting force decreases and provides an optimal cutting performance as compared to that in conventional side milling. First, the cross-sectional chip area is calculated using three-dimensional computer aided design (CAD) with its mean value relative to the cutting time. The ultrasonic vibration spindle apparatus is then attached to the machine spindle, and cutting tests are performed for conventional and ultrasonic vibration machining. Next, the flank wear, surface roughness, cutting force, and residual stress are measured. The results obtained from the cutting tests of the two machining methods are compared. The main results are as follows: (1) A comparison of the flank wears of conventional machining and ultrasonic vibration machining shows that the former is larger than the latter. The maximum flank wear increases as the cutting length increases for both the machining methods. (2) The maximum height of the machined surface in ultrasonic vibration machining is larger than that in conventional machining because of the marks caused by ultrasonic vibration. (3) The mean cross-sectional chip area relative to the cutting time decreases with ultrasonic vibration machining and the tool deformation decreases with a decrease in the mean cutting force relative to the cutting time. (4) With ultrasonic vibration machining, residual stress is generated on the machined surface not only in the feed direction but also in the axial direction because of the repetitive sliding actions in the axial direction of the flank of the cutting edge.

Are octahedral clusters missing on the carbon energy landscape?

We report a new class of carbon nanostructures at a lower sub-nano end of the size scale with a surprising stability, as compared to the well-known carbon fullerenes. The octahedral carbon clusters contain tetragonal rings, which, in spite of a common belief, prove to be an energy efficient means of plying graphene sheets to make three-dimensional spheroid shapes, similar to fullerenes. The two families of structures are shown to be competitive at small sizes (∼20 atoms) at room temperature, and for higher temperatures, at both small and large sizes (>200 atoms). Our calculations demonstrate that both vibrational and electronic spectra of these cluster families are similar, which thus might cloud their experimental identification. However, there is a sufficiently strong shift in vibrational frequencies below 160 and in the range of 600–800 cm−1, which should help to identify different types of carbon clusters experimentally. We propose octahedral clusters and other structures containing tetragonal rings as viable structural elements and building units in inorganic chemistry and materials science of carbon along with fullerenes.

Internal Morphology-Controllable Self-Assembly in Poly(Ionic Liquid) Nanoparticles.

Precise control of the interior and outer shapes of polymer nanoparticles has found broad interest in nanosciences, for example, in fundamental studies of their physical properties, colloidal behavior, and corresponding applications. Realizing such control below the 50 nm scale (i.e., a size scale close to individual polymer chains) requires accurate manipulation of polymerization techniques and a judicious choice of the chemical structure in monomers and/or polymers. Here, we constructed a series of well-defined sub-50 nm homopolymer nanoparticles with controllable shape and highly ordered, complex internal structures with sub-5 nm domain spacings, starting from 1-vinyl-1,2,4-triazolium-type ionic liquids in a one-pot dispersion polymerization. With cryogenic electron microscopy and tomography, a morphological evolution of particle shape and interior at this extremely small size end, unusual for polymer colloids, was identified and investigated in detail.

Dust production in debris discs: constraints on the smallest grains

The surface energy constraint puts a limit on the smallest fragment $s_{surf}$ that can be produced after a collision. Based on analytical considerations, this mechanism has been recently identified as been potentially able to prevent the production of small dust grains in debris discs and cut off their size distribution at sizes larger than the blow-out size. We numerically investigate the importance of this effect to find under which conditions it can leave a signature in the small-size end of a disc's particle size distribution (PSD). An important part of this work is to map out, in a disc at steady-state, what is the most likely collisional origin for micron-sized grains, in terms of the sizes of their collisional progenitors. We implement, for the first time, the surface energy constraint into a collisional evolution code. We consider a debris disc extending from 50 to 100AU and 2 different stellar types. We also consider two levels of stirring in the disc: dynamically "hot" (e=0.075) and "cold" (e=0.01). For all cases, we derive $s_{surf}$ maps as a function of target and projectile sizes, $s_t$ and $s_p$, and compare them to equivalent maps for the dust-production rate. We then compute disc-integrated PSDs and estimate the imprint of the surface energy constraint. We find that the ($s_p$,$s_t$) regions of high $s_{surf}$ values do not coincide with those of high dust production rate. As a consequence, the surface energy constraint has generally a weak effect on the system's PSD. The maximum $s_{surf}$-induced depletion of $\mu$m-sized grains is $\sim 30$% and is obtained for a sun-like star and a dynamically hot case. For the e=0.01 cases, the surface energy effect is negligible compared to the massive small grain depletion induced by another mechanism: the natural imbalance between dust production and destruction rates in low-stirring discs identified by Thebault&Wu(2008).

A dearth of small particles in debris disks

A prescription for the fragment size distribution resulting from dust grain collisions is essential when modelling a range of astrophysical systems, such as debris disks and planetary rings. While the slope of the fragment size distribution and the size of the largest fragment are well known, the behaviour of the distribution at the small size end is theoretically and experimentally poorly understood. This leads debris disk codes to generally assume a limit equal to, or below, the radiation blow-out size. We use energy conservation to analytically derive a lower boundary of the fragment size distribution for a range of collider mass ratios. Focussing on collisions between equal-sized bodies, we apply the method to debris disks. For a given collider mass, the size of the smallest fragments is found to depend on collision velocity, material parameters, and the size of the largest fragment. We provide a physically motivated recipe for the calculation of the smallest fragment, which can be easily implemented in codes for modelling collisional systems. For plausible parameters, our results are consistent with the observed predominance of grains much larger than the blow-out size in Fomalhaut's main belt and in the Herschel cold debris disks.

EVIDENCE FOR DUST EVOLUTION WITHIN THE TAURUS COMPLEX FROMSPITZERIMAGES

We present Spitzer images of the Taurus Complex (TC) and take advantage of the sensitivity and spatial resolution of the observations to characterize the diffuse IR emission across the cloud. This work highlights evidence of dust evolution within the translucent sections of the archetype reference for studies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100 um observations to produce a dust temperature map and a far-IR dust opacity map at 5' resolution. The average dust temperature is about 14.5K with a dispersion of +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger than the average value for the diffuse ISM. This opacity increase and the attenuation of the radiation field (RF) both contribute to account for the lower emission temperature of the large grains. The structure of the TC significantly changes in the mid-IR images that trace emission from PAHs and VSGs. We focus our analysis of the mid-IR emission to a range of ecliptic latitudes where the zodiacal light residuals are small. Within this cloud area, there are no 8 and 24 um counterparts to the brightest 160 um emission features. Conversely, the 8 and 24 um images reveal filamentary structure that is strikingly inconspicuous in the 160 um and extinction maps. The IR colors vary over sub-parsec distances across this filamentary structure. We compare the observed colors with model calculations quantifying the impact of the RF intensity and the abundance of stochastically heated particles on the dust SED. To match the range of observed colors, we have to invoke variations by a factor of a few of both the interstellar RF and the abundance of PAHs and VSGs. We conclude that within this filamentary structure a significant fraction of the dust mass cycles in and out the small size end of the dust size distribution.

Millisecond dip events in the 2007 RXTE/PCA data of Sco X—1 and the trans-Neptunian object size distribution

Abstract Millisecond dips in the RXTE/PCA archival data of Sco X-1 taken from 1996 to 2002 were reported recently. Those dips were found to be most likely caused by instrumental dead time but may also contain some true astronomical events, which were interpreted as the occultation of X-rays from Sco X-1 by trans-Neptunian objects (TNOs) of 100 m size. Here, we report the results of search for millisecond dip events with the new RXTE/PCA data of Sco X-1 taken in the year 2007. Adopting the same selection criteria as that in the previous study, we found only three dip events in 72-ks data, much fewer than the 107 events found in the 560-ks data taken from 1996 to 2002 reported earlier. The new data provide more detailed information of individual ‘very large events’ (VLEs), which is not available in the old archival data. Although the number of VLEs does not obviously increase during the occurrence of dip events, all the three dip events are coincident in time with VLEs that have no flags set for any of the propane or the six main xenon anodes. It is a strong indication of instrumental effects. No significant dips which might be real occultation by 60–100 m TNOs were observed. With only 72-ks data, however, the previously proposed possibility that about 10 percent of the dip events might not be instrumental still cannot be strictly excluded. Using the absence of those anomalous VLEs as the criterion for identifying non-instrumental dip events, we found, at a lower confidence level, four dip events of duration 8–10 ms in the 72-ks data. Upper limits to the size distribution of TNOs at the small size end are suggested.

Numerical simulation and sensitivity analysis of detailed soot particle size distribution in laminar premixed ethylene flames

In this paper, the prediction of a soot model [J. Appel, H. Bockhorn, M. Frenklach, Combust. Flame 121 (2000) 122–136] is compared to a recently published set of highly detailed soot particle size distributions [B. Zhao, Z. Yang, Z. Li, M.V. Johnston, H. Wang, Proc. Combust. Inst. 30 (2005)]. A stochastic approach is used to obtain soot particle size distributions (PSDs). The key features of the measured and simulated particle size distributions are identified and used as a simple way of comparing PSDs. The sensitivity of the soot PSDs to the parameters defining parts of the soot model, such as soot inception, particle and PAH collision efficiency and enhancement, and surface activity is investigated. Incepting soot particle size is found to have a very significant effect on the small-size end of the PSDs, especially the position of the trough for a bimodal soot PSDs. A new model for the decay in the surface activity is proposed in which the activity of the soot particle depends only on the history of that particle and the local temperature in the flame. This is a first attempt to use local flame variables to define the surface aging which has major impact on the prediction of the large-size end of the PSDs. Using these modifications to the soot model it is possible to improve the agreement between some of the points of interest in the simulated and measured PSDs. The paper achieves the task to help advance the soot models to predict soot PSD in addition to soot volume fraction and number density, which has been the focus of the literature.

Further studies on the smoothed SU(2) gauge configurations

The field variables (FV), the strength tensor (ST) and the topological charge density (TCD) of lattice SU(2) gauge field are studied in the momentum space. The evolution behaviors of their Fourier components are monitored during the smoothing procedure. The high frequency components of the FV can not be eliminated by smoothing, but all the Fourier amplitudes of the ST are uniformly suppressed. The distribution of the TCD in Euclidean spacetime is highly smoothed. Based on these facts, we give a new interpretation of the structure of the smoothed gauge configurations and argue that the ultraviolet and infrared cutoff introduced by lattice discretization account for the suppression of the instanton size distribution at both the large size end and the small size end.

Collisional evolution of asteroids

AbstractWe review the evidence for, and the modelling work devoted to, the substantial collisional evolution which has generated the current asteroid population and continually injects asteroid fragments into dynamicalroutesthrough which they can reach near-Earth space and sometimes hit our planet. The main obstacles to further progress in this research field are theoretical (mainly related to the physics of high-velocity impacts), but better observational data (in particular on the small-size end of the asteroid population) would help. However, in the last decade new insights have been obtained on specific important issues, such as the total mass of the asteroids at the time when the accretion process was stopped (only moderately larger than the current one), the “demography” of asteroid families (how many/how old they are and how they evolve) and the way meteorites and near-Earth asteroids are delivered/transported by a complex mixture of collisional and dynamical mechanisms.

Collisional Evolution of Trojan Asteroids

We model the collisional evolution of Trojan asteroids using a numerical code which combines recent calculations of the intrinsic collision probabilities and impact speeds in the Trojan swarms (Marzari et al.1996) with our current understanding of the outcomes of high-velocity collisions between asteroid-sized bodies. Using plausible collision parameters and energy scaling of impact strength with size, we obtain a good match to the present Trojan population, as inferred by Shoemaker et al.(1989). The steep slope of the current Trojan size distribution at diameters larger than about 50–100 km is essentially unaltered by the collisional process and must reflect the formative processes of these bodies. At smaller sizes, collisions have produced a power law size distribution having a slope characteristic of collisionally relaxed populations. Hence, we cannot distinguish whether the small-size end of the distribution was formed before or after the disruptive collisional regime characteristic of the present Trojan environment was established. The formation of prominent dynamical families in the Trojan swarms is a natural outcome of the collisional process; their number may allow us to constrain the degree of collisional evolution that has occurred in the Trojans. Finally, we find that Trojan collisional debris escaping from the libration regions and ending up into cometary orbits could supply ≈10% of the current population of short-period comets and Centaur asteroids. Whether this occurs depends on the dynamical lifetime of such bodies and whether they contain enough volatiles to become active comets.

The size distribution of interstellar dust particles as determined from polarization: Spheroids

view Abstract Citations (147) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Size Distribution of Interstellar Dust Particles as Determined from Polarization: Spheroids Kim, Sang-Hee ; Martin, P. G. Abstract We have determined the size distribution of polarizing interstellar dust grains based on electromagnetic scattering by spheroidal particles, extending our original work based on infinite cylinders. Shapes and alignment variants included the following: perfectly aligned oblate particles with axial ratios 1.414:1, 2:1, 4:1, and 6:1, picket fence prolate particles with axial ratios 2:1 and 4:1, and 2:1 prolate particles with perfect spinning alignment. Our analysis is based on bare silicate grains. The size distributions found are qualitatively similar to those derived using infinite cylinders. When expressed as contributions to the total mass, the distributions peak at mean size approximately 0.2 microns and are skewed, with the relative rate of decrease to larger and smaller sizes depending on lambda max. Using infinite cylinders, the specific requirement of a reasonable fit in the infrared produces a substantial dip in the mass distribution at approximately 0.4 microns, hinting at a bimodal mass distribution. But this dip is not present when oblate and prolate particles are used. This confirms that the dip is related to the incorrect behavior of scattering for infinite cylinders in the long wavelength limit. Fitting HST ultraviolet polarization data beyond 6 microns -1 introduces an additional bump at the small size end (approximately 0.01 microns) of the distribution. This unusual feature can be traced to the sudden rise in the imaginary part of the refractive index of 'astronomical silicate.' When a 'modified astronomical silicate' is used, the size of the additional bump is much reduced, if not absent. Based both on the smoothness of the mass distribution and on the fit to the polarization curve, oblate shapes are preferred to prolate. Among the oblates, the 6:1 oblate shape gives the most satisfactory result, simply because the width of the calculated polarization curve of single-sized 6:1 oblate particles is the narrowest. Mass distributions from fitting extinction curves using aligned spheroids have been determined. They resemble closely those based on spheres. Polarization to extinction ratios are large enough to match the maximum interstellar value for all axial ratios and shapes studied, though the most spherical (1.4:1 oblate and 2:1 spinning prolate) particles would have to be nearly perfectly aligned. The birefringence and interstellar circular polarization in the ultraviolet are predicted. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175604 Bibcode: 1995ApJ...444..293K Keywords: Cosmic Dust; Interstellar Matter; Particle Size Distribution; Polarization (Waves); Spheroids; Electromagnetic Scattering; Interstellar Extinction; Mass Distribution; Maximum Entropy Method; Astrophysics; ISM: DUST; EXTINCTION; POLARIZATION full text sources ADS | data products SIMBAD (5) MAST (1) ESA (1) Related Materials (2) Described in: 1979ApJ...228..450R Source Software: 2013ascl.soft11005M

Morphometric study of pillow-size spectrum among pillow lavas

Measurements of H and V (dimensions in the horizontal and vertical directions of pillows exposed in vertical cross-section) were made on 19 pillow lavas from the Azores, Cyprus, Iceland, New Zealand, Tasmania, the western USA and Wales. The median values of H and V plot on a straight line that defines a spectrum of pillow sizes, having linear dimensions five times greater at one end than at the other, basaltic toward the small-size end and andesitic toward the large-size end. The pillow median size is interpreted to reflect a control exercised by lava viscosity. Pillows erupted on a steep flow-foot slope in lava deltas can, however, have a significantly smaller size than pillows in tabular pillowed flows (inferred to have been erupted on a small depositonal slope), indicating that the slope angle also exercised a control. Pipe vesicles, generally abundant in the tabular pillowed flows and absent from the flow-foot pillows, have potential as a paleoslope indicator. Pillows toward the small-size end of the spectrum are smooth-surfaced and grew mainly by stretching of their skin, whereas disruption of the skin and spreading were important toward the large-size end. Disruption involved increasing skin thicknesses with increasing pillow size, and pillows toward the large-size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow. Pseudo-pillow structure is also locally developed. An example of endogenous pillow-lava growth, that formed intrusive pillows between ‘normal’ pillows, is described from Sicily. Isolated pillow-like bodies in certain andesitic breccias described from Iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions; it is now proposed that they may lack an essential attribute of pillows, namely, the development of bulbous forms by the inflation of a chilled skin, and are hence not true pillows. Para-pillow lava is a common lava type in the flow-foot breccias. It forms irregular flow-sheets that are locally less than 5 cm thick, and failed to be inflated to pillows perhaps because of an inadequate lava-supply rate or too high a flow velocity.