Interpulse Distance Research Articles

Parallel Diffractive Multi‐Beam Pulsed‐Laser Ablation in Liquids Toward Cost‐Effective Gram Per Hour Nanoparticle Productivity

Nanoparticles (NPs) generated by pulsed‐laser ablation in liquids (PLAL) have benefited many key applications due to their versatility, enlarged surface area, and high purity. However, scaling up NPs production represents one of the main requisites to commercialize this technology. The established upscaling strategy demands high power and repetition rate laser source with fast scanning systems, which are not widely available and costly. Herein, a cost‐effective alternative is proposed, the addition of static diffractive optical elements to achieve parallel processing through the multi‐beam PLAL (MB‐PLAL). In MB‐PLAL, the optimum repetition rate is reduced to compensate laser energy splitting, hence achieving a higher interpulse distance, reducing pulse shielding, and increasing NPs productivity. MB‐PLAL with 11 beams reached a factor 4 productivity increase for iron–nickel alloy (Fe50Ni50) NPs compared to the single‐beam setup (0.4–1.6 g h−1), and a factor 3 increase for gold (Au) NPs (0.32–0.94 g h−1). The scalability of the proposed MB‐PLAL technique setup is confirmed by Au and Fe50Ni50 NPs productivity experiments using 1, 6, and 11 beams, showing a linear increase in productivity.

Ultrashort pulse laser-induced submicron bubbles generation due to the near-surface material modification of soda-lime glass

Experimental evidence for near-surface micro- and nanoscopic processes at ultrashort pulsed laser irradiation(wavelength 775 nm, pulse duration 150 fs) of soda-lime glass near the laser ablation threshold is acquired by transmission electron and secondary electron microscopy (SEM, TEM) as well as by energy disperse x-ray spectroscopy (EDX) investigations of laser-induced subsurface bubbles. Well separated laser irradiations result in individual micrometre bubbles while submicron bubble groups or asymmetrically damaged bubbles appear for overlapping pulses. The overlapping laser irradiations result in a direction dependent damage for the successive bubbles when the inter-pulse distance is small. TEM/SEM studies of cross sectioned bubble prove that precipitations and jets are formed in the centre of the micron bubbles’ bottom. This nano-jets inside the bubble can be related to the self-focusing of the femtosecond laser. A modified layer with a composition deviation from the bulk glass can be a key factor for the formation of the bubble with a thin shell about 100 nm. Moreover, next to the central main bubble, nanometre sized bubbles appear below the surface. Thermal processes inside the bubble cause a smooth inner surface as well as redeposited material mainly opposite to the jet formed at the bottom. The different glass composition near the surface strongly suggests that the altered glass surface composition contributes to the forming mechanism of these near-surface features. Implications of these sub-surface bubbles and jet formation for laser ablation related applications comprise incubation as well as roughness development that limits the achievable precision.

Surface Height and Sea Ice Freeboard of the Arctic Ocean From ICESat‐2: Characteristics and Early Results

AbstractWe present the first winter season of surface height and sea ice freeboards of the Arctic Ocean from the new Ice, Cloud, and Land Elevation Satellite (ICESat‐2; IS‐2) mission. The Advanced Topographic Laser Altimeter System onboard has six photon‐counting beams for surface profiling with a 10‐kHz pulse rate (interpulse distance ~0.7 m) and footprints of ~17 m. Geolocated heights assigned to individual photons scattered from the surface allow significant flexibility in the construction of height distributions used in surface finding. For IS‐2 sea ice products, a fixed 150‐photon aggregate is used to control height precision and obtain better along‐track resolution over high reflectance surfaces. Quasi‐specular returns in openings as narrow as ~27 m, crucial for freeboard calculations, are resolved. The fixed photon aggregate results in unique variable along‐track resolutions and nonuniform sampling (17 m × 27 m to 17 m × 200 m for the strong beams) of the surface. The six profiling beams—three pairs separated by 3.3 km with a strong and weak beam in each pair—provide correlated statistics at regional length scales for assessment of beam‐to‐beam retrieval consistency and accuracy. Analysis shows along‐track height precisions of ~2 cm and agreement in the monthly freeboard distributions across the strong beams to 1–2 cm. In this paper, we describe briefly the approaches used in surface height and freeboard retrievals from Advanced Topographic Laser Altimeter System photon clouds and detail the key features of these along‐track sea ice products, focusing on the first release of data collected over the Arctic Ocean, which spans the period between 14 October 2018—the start of data collection—and the end of March 2019.

Living in sympatry via differentiation in time, space and display characters of courtship behaviors of bioluminescent marine ostracods

Distinguishing among courtship signals can be extremely important for individuals in regions where related species co-occur, including among sympatric species pairs and along hybrid zones. Reef habitats off the coast of Belize are shared by bioluminescent ostracods that perform nightly bioluminescent displays used in courtship. These displays vary in light pulse durations, interpulse distances and intervals, and direction. Here, we test how six sympatric species of marine ostracods (three described and three undescribed species) partition the display arena in time and space. Males from all six species can be differentiated based on morphology and species-specific luminescent display traits. Timing of nightly courtship display initiation and peak display timing differed among species by 5–25 min, and the order of appearance for each species was consistent across nights. In addition to varying temporally, species used different microhabitats (grassbed, sand channels, reef slopes and reef crest) for their courtship displays. Our findings support the hypothesis that species with more similar display traits (pulse duration, interpulse distance, number of pulses) differ most in the time and space used for courtship. The large number of axes for displacement of both luminescent display traits and spatio-temporal habitat use for courtship suggests that ostracods have the genetic toolkit for rapid diversification. This species complex living in sympatry yields a rich system for testing how genetic determination of behavioral traits relates to sexual selection and speciation.

Seismic communication in demon African mole rat Tachyoryctes daemon from Tanzania

We describe the production of substrate-borne vibrations in a subterranean mole rat of the genus Tachyoryctes for the first time. These signals with a supposed communication function were recorded using two approaches. Firstly, we recorded the production of spontaneous substrate-borne vibrations of individual test animals in artificial tunnels simulating a mole rat burrow system. Secondly, we recorded substrate-borne vibrations in individuals with interconnected home systems divided by a barrier. We found that Tachyoryctes produces these seismic signals by striking its head against the ceiling of the tunnel. Two types of seismic signals differing in physical parameters were identified. A slow signal (inter-pulse distance 0.12 s, inter-bout distance 3.89 s, number of pulses within each bout 9.53) was produced in both experiments, whereas a fast signal (inter-pulse distance 0.05 s, inter-bout distance 18.44 s, number of pulses within each bout 22.54) was produced mainly in close proximity to another individual. Our results indicate that fast signals are probably individually specific, because the success rate of classification according to discriminant function analysis was 70.4 % for the three tested individuals.

Steady-state indicators of the intracranial pressure dynamic system using geodesic distance of the ICP pulse waveform

Normal functioning of the brain depends on the homeostasis (∼ steady state) of its various physiological sub-systems, one of which is the intracranial pressure (ICP) dynamic system. The ICP dynamic system of an injured brain is susceptible to various acute changes that should ideally be detected by ICP monitoring even for comatose patients. However, the status quo of ICP monitoring solely targets mean ICP. We aimed to demonstrate a novel approach to detect acute deviation from steady state of an ICP dynamic system in an absence of significant mean ICP changes. We hypothesized that steady state of ICP dynamic systems is reflected as ICP pulses of similar mean ICP levels resembling each other for a given subject. A general framework was used to derive such a steady-state indicator that can accommodate different metrics of inter-pulse distance and different statistics of the distance histograms. In addition to conventional Euclidean distance and Pearson correlation, geodesic distance between pulses was introduced as a novel metric. These different ways of calculating steady-state indicators under the proposed framework were evaluated on three types of continuous ICP recordings: (1) those between two consecutive brain imaging studies that demonstrated acute ventricular enlargement for slit ventricle syndrome (SVS) patients undergoing a trial of shunt externalization and clamping (SVS+); (2) those between consecutive brain imaging studies from the SVS patients under the same trial but without ventricular enlargement (SVS−); (3) overnight recordings from normal pressure hydrocephalus (NPH) patients. It was observed that only the standard deviation of geodesic distance correctly differentiated between SVS+ and SVS− and between SVS+ and NPH while avoiding discriminating between SVS− and NPH. It was also found that 45% SVS+ cases had a multimodal geodesic distance histogram while none of SVS− and 3.8% of NPH cases had such a multimodal histogram. Pulses with a large number of distant pulses for the five multimodal-histogram SVS+ cases fell in short time windows indicating that acute ventricular changes may have occurred in these confined time windows during which no significant changes of mean ICP were observed. In contrast, the pulses with a large number of distant pulses for the two multimodal-histogram NPH cases did not cluster temporally. In conclusion, the geodesic inter-pulse distance is a promising metric to quantify distance intrinsic to the underneath geometric structure of ICP signals and hence is a more suitable way to derive a steady-state indicator of an ICP dynamic system.

Sequencing the unsequenceable: Expanded CGG-repeat alleles of the fragile X gene

The human fragile X mental retardation 1 (FMR1) gene contains a (CGG)n trinucleotide repeat in its 5′ untranslated region (5′UTR). Expansions of this repeat result in a number of clinical disorders with distinct molecular pathologies, including fragile X syndrome (FXS; full mutation range, greater than 200 CGG repeats) and fragile X–associated tremor/ataxia syndrome (FXTAS; premutation range, 55–200 repeats). Study of these diseases has been limited by an inability to sequence expanded CGG repeats, particularly in the full mutation range, with existing DNA sequencing technologies. Single-molecule, real-time (SMRT) sequencing provides an approach to sequencing that is fundamentally different from other “next-generation” sequencing platforms, and is well suited for long, repetitive DNA sequences. We report the first sequence data for expanded CGG-repeat FMR1 alleles in the full mutation range that reveal the confounding effects of CGG-repeat tracts on both cloning and PCR. A unique feature of SMRT sequencing is its ability to yield real-time information on the rates of nucleoside addition by the tethered DNA polymerase; for the CGG-repeat alleles, we find a strand-specific effect of CGG-repeat DNA on the interpulse distance. This kinetic signature reveals a novel aspect of the repeat element; namely, that the particular G bias within the CGG/CCG-repeat element influences polymerase activity in a manner that extends beyond simple nearest-neighbor effects. These observations provide a baseline for future kinetic studies of repeat elements, as well as for studies of epigenetic and other chemical modifications thereof.

Pulsed Laser Ablation of Zinc in Tetrahydrofuran: Bypassing the Cavitation Bubble

We applied a high-power (25 W) picosecond-pulsed laser system in combination with fast scanner optics for pulsed laser ablation in liquids in order to generate zinc/zinc oxide nanoparticles in tetrahydrofuran with optimized efficiency. Systematic variation of repetition rate and interpulse distance of subsequent laser pulses strongly affects the ablation efficiency. Shielding of subsequent laser pulses by induced cavitation bubbles could be minimized by these parameters. The analysis of experimental data results in a time constant of 55 μs concerning the cavitation bubble decay and a nonspherical shape with a lateral elongation of 120 μm after 100 μs. Regarding these parameters allows temporal and spatial bypassing of the cavitation bubble to enhance ablation efficiency and nanoparticle productivity. Furthermore, there is a nonlinear dependency of ablation efficiency on interpulse distance even if an effect coupled by cavitation bubbles can be excluded. We interpret this as a competition between two ablation mechanisms including thermal vaporization and phase explosion. For that purpose, we assume a transient preheating of the target by previous pulse, which leads to less efficient heat conduction that favors phase explosion instead of thermal vaporization. Calculations of 1D-heat conduction and analysis of generated nanoparticles support that interpretation. We were able to model the shape of the cavitation bubble and the experimental data by an adopted fit function.

Ablation efficiency of α-Al2O3 in liquid phase and ambient air by nanosecond laser irradiation

Ablation efficiency and influences of laser parameters on a material removal rate by a nanosecond laser irradiation of α-Al2O3 are studied in gas and liquid phases. The laser ablation in the air yields maximum material removal rate of 12 ng/pulse using a 4.6-mJ pulse energy at 4-kHz repetition rate, compared to 88 ng/pulse in the water flow. Using a specific interpulse distance and a laser repetition rate further increase material removal rate by factor of 3 and 65, respectively, owing to an optimized lattice temperature and laser pulse interactions with the generated cavitation bubble. For the ablation in the air, these parameters do not significantly affect the ablation efficiency.

Gram Scale Synthesis of Pure Ceramic Nanoparticles by Laser Ablation in Liquid

Scale-up criteria of laser ablation in the liquid phase with nanosecond pulses is studied for efficient generation of pure ceramic nanoparticles in an aqueous environment. Besides high laser fluence and low height of the applied liquid layer, specific pulse overlap and defined laser repetition rate are required for significant enhancement in nanoparticle productivity. The ablation rate increases by 350% by reducing the liquid film from 8 mm to 2.5 mm owing to reduced absorption and scattering of the incident laser beam by previously ablated nanoparticles. The controlled interpulse distance yields a further increase in material removal rate by another 300% compared to machining in the pulse overlap mode. The residual cavitation bubble from the previous laser pulse and the dispersed nanoparticle interaction with the following laser pulse and optimized temperature gradient in the lattice of the target are assumed to alter productivity. This hypothesis is confirmed by varying the repetition rate with equal la...

It's All About Sex: Bioluminescent Courtship Displays, Morphological Variation and Sexual Selection in Two New Genera of Caribbean Ostracodes

A large clade of cypridinid ostracodes, found only in the Caribbean, uses species specific courtship displays of secreted luminescence, produced by males, to attract photically silent females to mate. We recently described two new genera, Photeros and Enewton, which are part of this clade (Cohen and Morin, 2010). Within the various subclades of these signaling ostracodes in the Caribbean, onlyPhoteros has been shown to have species-specific differences in both their luminescent displays and the morphology of the large male copulatory (eighth) limb (Cohen and Morin, 2010). The apparent ancestral display pattern, which occurs among at least some species in all the signaling clades of Caribbean ostracodes, is produced as a series of pulses of light secreted into the water column mostly in a vertical pattern, either upward or downward, above species-specific habitats. The pulses are of fairly long duration and become shorter and closer together. A derived pattern of very rapid pulses, which also shows within train interpulse distance shortening, is found only in the genusPhoteros. It is likely that the high diversity found in this clade and other signaling clades has been driven by their life history patterns in conjunction with sexual selection acting via the courtship displays and their reproductive structures.

Multiuser performance of M-ary orthogonal coded/balanced UWB transmitted-reference systems

A tractable and compact closed-form expression on the channel-averaged signal-to-interference-plus-noise ratio (SINR) is derived for M-ary orthogonal coded/balanced transmitted-reference (BTR) systems, taking into consideration both inter-pulse interference (IPI) and multiple-access interference (MAI) in dense multipath ultra-wideband (UWB) channels. The UWB channel here is a realistic and standard one with lognormal channel gain distribution and double independent Poisson arrival distribution of cluster and ray. Hence, the analytical framework developed here can be applied to typical UWB channel models, especially considering the channel sparseness and cluster overlapping observed in realistic UWB channels. Based on the channel-averaged SINR, the effect of inter-pulse distance (between the reference and data pulses in BTR) on the multiuser performance is fully investigated. A proper selection of user-specific inter-pulse distances in multiuser scenario is then determined to maximize the user capacity for a given UWB channel.

Multiple Access Performance of Balanced UWB Transmitted-Reference Systems in Multipath

Recently, a novel balanced transmitted-reference (TR) system has been proposed for UWB communications. This TR system is capable of properly eliminating the inter-pulse interference (IPI) between the reference and data pulses in a single user multipath environment. In this paper, we investigate its multiple access (MA) performance by evaluating the second- order moments of noise and interference terms. The analytical framework developed here can also be used to accurately evaluate the MA performance of conventional TR system. It is shown that the proposed balanced TR system can achieve comparable MA capacity as conventional TR, while operating at higher information rate. On the other hand, given a target information rate, the balanced TR system in conjunction with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary signaling offers higher MA capacity than conventional TR system. The performance results suggest there exists a trade-off between the inter-pulse distance, thus the achievable information rate, and the MA capacity.

Extended Dust Shells around Carbon Stars in the Infrared and in Optical Light

We investigate the structure of extended dust shells around optical carbon stars in the far-infrared and in optical light. In the optical we have discovered that R Scl and U Ant are associated with circularly extended emission, the radii of which are about 20″ and 58″, respectively. The emission is probably scattered light of the central star by dust grains in their circumstellar shells. In the far-infrared we have discovered a double shell structure surrounding U Ant in high resolution IRAS images, which is direct evidence of a periodic change of mass-loss on a time-scale of the order of 104 years in the AGB evolution. Relating the two shells to two consecutive thermal pulses allows for a self-consistent determination of the interpulse period, core-mass, luminosity, and distance. Direct mapping of Y CVn at 90 and 160 μm with ISOPHOT on board ISO has revealed a very extended detached dust shell around this star. The mass-loss rate is found to have decreased drastically by two orders of magnitude 1.4×104 years ago, which should be an important clue to the understanding of J-type stars.

Collinear filter controlled by variable ultrasonic pulses

The experimental investigation of the problem of collinear acousto-optic tunable filters driven by variable acoustic pulses is carried out. It is shown that bandwidth and shape of transmission function can be altered in this case by varying the shape of a driving pulse. Experi- mental acousto-optic tunable filter transmission curves and their side wings are presented. It is shown that the utilization of pulses with a smooth temporal envelope results in a decrease of sidelobe level in the acousto-optic tunable filter transmission curves. It is found that the dif- fracted light can be generated continuously if the interpulse distance is equal to the crystal length. The transmission bandwidth in this case is determined by the length of each acoustic pulse. The impact of the phase difference between acoustic pulses on the diffraction efficiency and on the diffracted light form is investigated. © 1999 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(99)00307-4)

Rate of realized interception of pheromone pulses in different wind speeds modulates almond moth orientation

The interception of a pheromone filament induces flying moths to surge briefly nearly straight upwind; in the absence of pheromone moths cease upwind progress and zigzag crosswind. We tested males of the almond moth, Cadra cautella (Lepidoptera, Pyralidae), in a low-turbulence wind tunnel in wind velocities of 20, 40 and 80 cm s−1. A mechanical pulse generator was set to produce plumes either with same pheromone pulse frequency (pulse generation frequency of 2.9 Hz, interpulse distances from 7 cm to 28 cm) or plumes with same interpulse distance across the three wind velocities (interpulse distance of 14 ± 2 cm, pulse generation frequency of 1.7–5.0 Hz). In plumes of similar pulse frequency, the faster the speed of the wind the slower the ground speed of flight. However, in plumes of similar interpulse distance, ground speed remained relatively constant independent of the wind speed. A `realized' frequency of pulse interception for males flying along the various combinations of pulse frequencies and wind velocities was calculated using the males' average airspeed and the spatial distribution of pheromone pulses in the plume. Realized frequency of pulse interception ranged from 1.3- to 3.0-fold higher than the frequency of pulse generation. The flight tracks of males reflected the regime of realized pulse interception. These results suggest that upwind flight orientation of male C. cautella to pheromone in different wind velocities is determined by the flux of filament encounter.