Ablation Event Research Articles

Novel Method for Risk Stratification of Major Adverse Clinical Events Using Pre- and Post-Ablation Left Atrial Volume Index in Patients With Persistent Atrial Fibrillation.

The relationship between changes in the left atrial volume index (LAVI) post-catheter ablation (CA) and long-term prognostic events in patients with persistent atrial fibrillation (AF) remains unclear. We evaluated the incidence of major adverse clinical events (MACE), including all-cause death, unplanned heart failure hospitalization, and unplanned cardiovascular hospitalization using pre- and post-CA LAVI. We collected data retrospectively from 150 patients with persistent AF who underwent their first CA. LAVI was calculated during preprocedural echocardiography under AF rhythm (pre-CA LAVI) and 3 months post-CA under sinus rhythm (post-CA LAVI). The cumulative incidence of MACE was compared among 3 subgroups based on the cutoff values of pre-CA (45.5 mL/m2) and post-CA (46.5 mL/m2; both determined using the c-statistic) LAVI. The subgroup of a pre-CA LAVI >45.5 mL/m2 with a post-CA LAVI >46.5 mL/m2 (n=45) had a significantly higher MACE incidence compared with other subgroups (P=0.002). Multivariate analysis identified this subgroup as independently at higher risk for MACE. The subgroup of a pre-CA LAVI >45.5 mL/m2 with a post-CA LAVI ≤46.5 mL/m2 (n=49) had an incidence comparable with those with pre-CA LAVI ≤45.5 mL/m2 (n=56) and exhibited a significantly greater reduction in LAVI than other subgroups did (P<0.001). Combining pre-CA and post-CA LAVIs is valuable in stratifying long-term MACE development risk following CA.

MRI-guided transrectal prostate laser ablation for benign prostatic hypertrophy: a retrospective cohort study.

To investigate whether MRI-guided transrectal laser ablation is safe and effective for the treatment of lower urinary tract symptoms caused by BPH. This single-center retrospective cohort study evaluated men who underwent MRI-guided transrectal laser ablation for BPH between February 2017 and July 2021. Age, prostate-specific antigen, prostate volume, prior surgical BPH treatments if any, International Prostate Symptom Score (IPSS) and Sexual Health Inventory of Men (SHIM) were collected. The primary outcome measures assessed were change in IPSS and SHIM 6, 12 and 24 months after laser ablation and adverse events. Fifty-two patients were included, having completed at least one follow-up survey. The mean patient age was 62.9 ± 5.7 years, and mean prostate volume was 80.2 ± 39.2 cc. Eighteen patients (34.6%) had received a prior BPH treatment. The IPSS scores dropped an average of 16.7 ± 7.0 (p < 0.001), 16.9 ± 7.5 (p < 0.001) and 17.1 ± 7.2 (p < 0.001) points from baseline at 6, 12 and 24 months, respectively. There was no statistically significant difference in IPSS score drop between patients who had received a prior BPH procedure and those who had not (p = 0.628). The SHIM scores showed a statistically insignificant increase at all time points. Nineteen patients (36.5%) reported a complication. There were 12 grade II complications (23%) and seven grade I complications (13.5%). There were no grade III or higher complications. Transrectal MRI-guided focal laser ablation is safe and effective for the treatment of lower urinary tract symptoms caused by BPH, with a significant improvement in symptom severity after 2 years.

Analysis of the periodic variation of pellet ablation radiation intensity in ASDEX Upgrade

Abstract In a future fusion reactor, the main fuelling method will likely rely on the injection of solid hydrogen pellets. Current predictions assume that this goal can be achieved, since being based on a technology which is already largely developed. However, this belief is founded on modelling tools that are usually aligned to the observation made in existing devices and then extrapolated to reactor conditions. This approach needs a sound consideration of its intrinsic restrictions and any observed feature not reproduced by the utilised codes should be applied to check their validation and possibly contribute to their refinement. One specific feature still lacking an explanation of a reasonable and self-consistent mechanism in the current models is the appearance of a phenomenon called striations, which are high frequency variations in the radiation emitted during the pellet ablation process. In order to provide a sound and reliable database for further considerations, a dedicated analysis of this effect has been performed on the mid-size tokamak ASDEX Upgrade. Therefore, such cases have been selected with the relevant signal recorded with sufficient temporal resolution during experiments covering a wide variation of plasma and pellet parameters which are regarded to be potentially influential on the striation pattern. In addition, it was ensured that for any specific case the observed behaviour was reproducible for several individual ablation events under identical conditions. In all cases considered, the observed radiation-intensity variations appear with a typical pattern showing a broad peak of frequencies in the range 50 to 150 kHz. This characteristic unveils a notable resilience against any parameter variation. This new collection of data can now act as firm basis to corroborate future modelling code-validation efforts. In addition, the analysis method can provide a relatively simple way of reviewing future modelling predictions.

Ohio River basin snow ablation and the role of rain‐on‐snow

AbstractSnow cover ablation within the Ohio River Basin (ORB) plays an important role in regional hydroclimatology, while also representing a potential hazard during large and rapid events. Rain‐on‐snow ablation is a particular challenge, where runoff rates are typically enhanced due to the dual inputs of snowmelt and liquid precipitation. Here, we present a 40‐year climatology of snow ablation events frequency, intensity, and timing for the ORB using a 4‐km gridded snow‐water‐equivalent dataset, focusing on the relative proportion of events caused by rain‐on‐snow and changes over time. Spatial patterns of snow ablation frequency and intensity mirror that of seasonal snowfall totals, with higher (lower) values in the northern and eastern (southern) portions of the basin. Rain‐on‐snow events represent approximately 40% of all ablation events within the basin and result in approximately 24%–25% more snow‐water‐equivalent loss than non‐rain‐on‐snow events, plus an additional 3–12 mm of liquid precipitation per event on average. Peak frequency of ablation and rain‐on‐snow events occurs in late winter and early spring, similar to that of the surrounding region. Over time, the frequency of ablation and rain‐on‐snow events has decreased in the northern and eastern portions of the basin, in some cases by as much as 30%. Trends in event magnitudes were more isolated but decreased across portions of central IN, northern KY, eastern OH and northern WV. Additionally, the magnitude of precipitation during rain‐on‐snow events has increased across the region, extending from northern KY into western PA by over 100% in many cases. Broadly, we find tendencies towards fewer events with less snow loss but more liquid precipitation that suggest complicated impacts to the hydroclimatology warranting further investigation.

Catalytic Pyrolysis of Polypropylene for Cable Semiconductive Buffer Layers.

With the progress of the power grid system, the coverage area of cables is widening, and the problem of cable faults is gradually coming to affect people's daily lives. While the vast majority of cable faults are caused by the ablation of the cable buffer layer, polypropylene (PP), as a common cable buffer material, has pyrolysis properties that critically impact cable faults. Studying the semiconductive buffer layer of polypropylene (PP) and its pyrolysis properties allows us to obtain a clearer picture of the pyrolysis products formed during PP ablation. This understanding aids in the accurate diagnosis of cable faults and the identification of ablation events. In this study, the effects of temperature and catalyst (H-Zeolite Standard Oil Corporation Of New York (Socony) Mobil-Five (HZSM-5)) content on the PP thermolysis product distribution were studied by using an online tubular pyrolysis furnace-mass spectrometry (MS) experimental platform. The results showed that PP/40% HZSM-5 presented the highest thermolytic efficiency and relative yield of the main products at 400 °C.

Atmospheric Drivers Associated with Extreme Snow Ablation and Discharge Events in the Susquehanna River Basin: A Climatology

Abstract Extreme snow ablation can greatly impact regional hydrology, affecting streamflow, soil moisture, and groundwater supplies. Relatively little is known about the climatology of extreme ablation events in the eastern United States, and the causal atmospheric forcing mechanisms behind such events. Studying the Susquehanna River basin over a 50-yr period, here we evaluate the variability of extreme ablation and river discharge events in conjunction with a synoptic classification and global-scale teleconnection pattern analysis. Results indicate that an average of 4.2 extreme ablation events occurred within the basin per year, where some 88% of those events resulted in an increase in river discharge when evaluated at a 3-day lag. Both extreme ablation and extreme discharge events occurred most frequently during instances of southerly synoptic-scale flow, accounting for 35.7% and 35.8% of events, respectively. However, extreme ablation was also regularly observed during high pressure overhead and rain-on-snow synoptic weather types. The largest magnitude of snow ablation per extreme event occurred during occasions of rain-on-snow, where a basinwide, areal-weighted 5.7 cm of snow depth was lost, approximately 23% larger than the average extreme event. Interannually, southerly flow synoptic weather types were more frequent during winter seasons when the Arctic and North Atlantic Oscillations were positively phased. Approximately 30% of the variance in rain-on-snow weather type frequency was explained by the Pacific–North American pattern. Evaluating the pathway of physical forcing mechanisms from regional events up through global patterns allows for improved understanding of the processes resulting in extreme ablation and discharge across the Susquehanna basin. Significance Statement The purpose of this study is to better understand how certain weather patterns are related to extreme snowmelt and streamflow events and what causes those weather patterns to vary with time. This is valuable information for informing hazard preparation and resource management within the basin. We found that weather patterns with southerly winds were the most frequent patterns responsible for extreme melt and streamflow, and those patterns occurred more often when the Arctic and North Atlantic Oscillations were in their “positive” configuration. Future work should consider the potential for these patterns, and related impacts, to change over time.

Three-Dimensional Numerical Modeling of Ground Ice Ablation in a Retrogressive Thaw Slump and Its Hydrological Ecosystem Response on the Qinghai-Tibet Plateau, China

Retrogressive thaw slumps (RTSs), which frequently occur in permafrost regions of the Qinghai-Tibet Plateau (QTP), China, can cause significant damage to the local surface, resulting in material losses and posing a threat to infrastructure and ecosystems in the region. However, quantitative assessment of ground ice ablation and hydrological ecosystem response was limited due to a lack of understanding of the complex hydro-thermal process during RTS development. In this study, we developed a three-dimensional hydro-thermal coupled numerical model of a RTS in the permafrost terrain at the Beilu River Basin of the QTP, including ice–water phase transitions, heat exchange, mass transport, and the parameterized exchange of heat between the active layer and air. Based on the calibrated hydro-thermal model and combined with the electrical resistivity tomography survey and sample analysis results, a method for estimating the melting of ground ice was proposed. Simulation results indicate that the model effectively reflects the factual hydro-thermal regime of the RTS and can evaluate the ground ice ablation and total suspended sediment variation, represented by turbidity. Between 2011 and 2021, the maximum simulated ground ice ablation was in 2016 within the slump region, amounting to a total of 492 m3, and it induced the reciprocal evolution, especially in the headwall of the RTS. High ponding depression water turbidity values of 28 and 49 occurred in the thawing season in 2021. The simulated ground ice ablation and turbidity events were highly correlated with climatic warming and wetting. The results offer a valuable approach to assessing the effects of RTS on infrastructure and the environment, especially in the context of a changing climate.

Pulsed laser ejection of single-crystalline III-V solar cells from GaAs substrates

The best III-V solar cells start out as single-crystalline multilayers on GaAs substrates. Separating these multilayers from their growth substrate enables higher performance and wafer reuse, which are both critical for terrestrial III-V solar cell viability. Here, we remove rigidly bonded, 16 mm2 × 3.5 μm thick devices from a GaAs substrate using an unfocused Nd:YAG laser pulse. The pulse is absorbed by a low-band-gap, lattice-matched layer below the device, driving an ablation event that ejected the crystalline multilayer from the substrate. Minutes of selective wet-chemical etching and device finishing yield a 0.1 cm2 device with a 17.4% power conversion efficiency and open-circuit voltage of 1.07 V, using AM1.5 direct with no anti-reflection coating. We show that the performance is comparable to similar cells produced via conventional processes. We discuss unique process characteristics, such as the potential to separate wafer-sized solar cells per laser pulse.

Abstract 15093: Elevated Risk of Recurrent Ablation in Black Compared to White Patients With Atrial Fibrillation: Another Paradox of Atrial Fibrillation in Blacks

Introduction: Lower prevalence of atrial fibrillation (AF) despite a higher prevalence of risk factors in blacks compared to whites (AF paradox) has been reported. However, less information is available about recurrent ablation events in blacks compared to whites. Methods: Demographic characteristics and one-year recurrent ablation events were analyzed in AF patients admitted to a community hospital from 2018 to 2021. Results: Recurrent AF ablation occurred in 3.7% (16/435) of the study population and was significantly higher in black compared to white patients [9/86 (10.5%) vs. 7/349 (2.0%), respectively, p=0.0001]. Black race and history of atrial flutter were predictors of recurrent AF ablation (p&lt;0.05) within one year of initial ablation. Black patients were younger (p=0.03) with a significantly higher prevalence of hypertension, diabetes, cardiomyopathy/heart failure, thyroid disease, renal disease, sleep apnea, COVID-19, pacemaker/AICD placement, and history of Ventricular tachycardia (Table). Concomitant medications were similar between races besides higher use of antihypertensive medications in black patients (Table). Conclusions: In our community hospital setup, black patients with AF had a higher prevalence of comorbidities and significantly higher incidence of one-year recurrent ablation events despite similar therapy compared to white patients. These observations should be explored in a larger prospective study to understand the differential association of comorbidities in black AF patients and associated higher risk for recurrent events.

Persistent influence of precession on northern ice sheet variability since the early Pleistocene

Prior to ~1 million years ago (Ma), variations in global ice volume were dominated by changes in obliquity; however, the role of precession remains unresolved. Using a record of North Atlantic ice rafting spanning the past 1.7 million years, we find that the onset of ice rafting within a given glacial cycle (reflecting ice sheet expansion) consistently occurred during times of decreasing obliquity whereas mass ice wasting (ablation) events were consistently tied to minima in precession. Furthermore, our results suggest that the ubiquitous association between precession-driven mass wasting events and glacial termination is a distinct feature of the mid to late Pleistocene. Before then (increasing), obliquity alone was sufficient to end a glacial cycle, before losing its dominant grip on deglaciation with the southward extension of Northern Hemisphere ice sheets since ~1 Ma.

North American rain-on-snow ablation climatology

Rain-on-snow ablation events carry a relatively high risk for rapid snowmelt and runoff due to the combination of liquid precipitation and generally high turbulent fluxes into the snowpack. Determining the variability in rain-on-snow ablation is critical in describing local hydroclimate. This study uses a gridded observational snow dataset to examine spatiotemporal variations in North American rain-on-snow ablation over a 50 yr period. Here we show rain-on-snow ablation represents approximately 33% of all ablation events in the eastern third of the continent, compared to &lt;20% in its interior. Rain-on-snow ablation was most frequent along the western and eastern coasts of the continent, with &gt;10 events observed per year on average. A central band of enhanced event frequencies propagated meridionally during the calendar year, most prominently in the eastern half of the continent. Seasonal (September to August) event frequency from 1960-2009 significantly decreased by approximately 50% across much of northern Quebec and in the southern Appalachians, while it significantly increased in portions of British Columbia and southeastern Quebec. Interannual variations in event frequency were primarily forced by variations in seasonal-scale snowfall and snow depth, and only moderately associated with variations in air temperatures.

Radiofrequency ablation to achieve durable pulmonary vein isolation.

Pulmonary vein isolation (PVI) by radiofrequency (RF) ablation is an important alternative to antiarrhythmic drugs in the treatment of symptomatic atrial fibrillation. However, the inability to consistently achieve durable isolation of the pulmonary veins hampers the long-term efficacy of PVI procedures. The large number of factors involved in RF lesion formation and the complex interplay of these factors complicate reliable creation of durable and transmural ablation lesions. Various surrogate markers of ablation lesion formation have been proposed that may provide information on RF lesion completeness. Real-time assessment of these surrogates may aid in the creation of transmural ablation lesions, and therefore, holds potential to decrease the risk of PV reconnection and consequent post-PVI arrhythmia recurrence. Moreover, titration of energy delivery until lesions is transmural may prevent unnecessary ablation and subsequent adverse events. Whereas several surrogate markers of ablation lesion formation have been described over the past decades, a 'gold standard' is currently lacking. This review provides a state-of-the-art overview of ablation strategies that aim to enhance durability of RF-PVI, with special focus on real-time available surrogates of RF lesion formation in light of the biophysical basis of RF ablation.

Prognostic value of pharmacotherapy in patients with atrial fibrillation after radiofrequency ablation

The aim of the work: to evaluate the prognostic effect of pharmacotherapy before and after radiofrequency ablation (RFA) in patients with atrial fibrillation (AF) on all-cause mortality, supraventricular arrhythmia recurrence and non-fatal cardiovascular events. Materials and methods. Patients with paroxysmal, persistent and long-term persistent forms of AF were examined before and after RFA – isolation of pulmonary veins. The primary endpoint was patient survival, secondary – a composite endpoint of freedom from recurrence and/or non-fatal cardiovascular events for 2 years of a follow-up. Frequency and doses of pharmacotherapy were evaluated. Standard statistical procedures were used for initial data evaluation. Results. 116 patients were consecutively enrolled in the study. In the long-term post-ablation, 23 patients (19.8 %) continued to take amiodarone, 2 patients (1.7 %) – propafenone for arrhythmic events, 38 patients (32.8 %) needed anticoagulants, and 37 patients (31.9 %) received beta-adrenoceptor blockers over the entire follow-up period. The use of RAAS inhibitors decreased from 81.0 % before the ablation to 56.0 % in the long-term period following RFA. Multifactorial logistic regression analysis showed that the prolonged (more than 3 months) anticoagulation (P = 0.032) after RFA was an independent predictor of patient survival in the two-year follow-up; doses of anticoagulants before the procedure, use and doses of beta-adrenoceptor blockers in the long-term post-ablation period were associated with the secondary endpoint. Conclusions. RFA for AF significantly reduced the frequency of medications use in the long-term postoperatively. Independent predictors of survival were the doses of anticoagulants more than 3 months after ablation, arrhythmia recurrence and non-fatal cardiovascular events – the doses of anticoagulants before the procedure, and the use and doses of beta-adrenoceptor blockers in the long-term period after RFA.

Emission characteristics and dynamics of neutral, ionic and molecular species in a laser produced CaF2 plasma

The emission characteristics of a laser-ablated calcium fluoride CaF2 plasma have been investigated using time and space optical emission spectroscopy. The plasma-plume was produced by focusing 266 nm, 15 ns pulses from a Nd: YAG laser on a calcium fluoride crystal substrate placed in a vacuum chamber. The emission observed in the plasma region is due to electronic relaxation of excited neutral Ca and F, ionic fragments Ca2+, Ca+ and F+ and molecular features of CaF (A2Π- X2Σ+, B2Σ+- X2Σ+ and C2Π- X2Σ+) band systems. Plasma species were analyzed both as a function of the delay from the laser pulse incidence and location from the target surface. Spectroscopic diagnostics were employed to estimate time-resolved electron densities, electron temperatures and velocity expansion of different species. The results show a faster decay of the continuum emission, ionic F+, Ca2+, Ca+, F species than in the case of neutral Ca atoms and molecular species of CaF. Different excitation temperatures were measured by comparing Ca and F atomic/ionic Saha-local thermodynamic equilibrium (LTE) spectra with experimental ones at various delay times after the ablation event. Vibrational temperatures of CaF were assessed from the temporal analysis of the A2Π - X2Σ+ Δv = 0 band sequence molecular emission. We observed a non-equilibrium plasma although the plasma is found to maintain partial LTE.

A Detailed, Multi‐Scale Assessment of an Atmospheric River Event and Its Impact on Extreme Glacier Melt in the Southern Alps of New Zealand

AbstractNorth‐westerly airflow and associated atmospheric rivers (ARs) have been found to profoundly influence New Zealand’s west coasts, by causing flooding, landslides and extreme ablation and accumulation on glaciers in the Southern Alps. However, the response of local glacier mass balance to synoptic‐scale circulation, including events with ARs, has typically not been investigated by considering mesoscale processes explicitly. In this study, high‐resolution atmospheric simulations from the Weather Research and Forecasting model are used to investigate the mesoscale drivers of an extreme ablation event on Brewster Glacier (Southern Alps), which occurred on February 6, 2011 during the landfall of an AR on the South Island. The following processes were found to be crucial for transferring the high temperature and water vapor contained in the AR into energy available for melt on Brewster Glacier: First, the moist‐neutral character of the air mass enabled the flow to pass over the ridge, leading to the development of orographic clouds and precipitation on the windward side of the orography, and foehn winds on the leeside. These processes fueled melt through longwave radiation and strong turbulent and rain heat fluxes within the high‐condensation environment of the orographic cloud. Second, orographic enhancement occurred due to both cellular convection within the cloud and the combined effect of multiple precipitating systems by the seeder‐feeder‐mechanism. These results indicate the potential importance of AR dynamics for New Zealand’s glaciers. They also illustrate the benefit of mesoscale atmospheric modeling for advancing process understanding of the glacier‐climate relationship in New Zealand.

Declining North American snow cover ablation frequency

AbstractAt a continental scale, trends in aggregate ablation frequency inform changes in snow cover extent, however the variability and trends in the frequency and magnitude of snow ablation events at regional scales are less well understood. Determining such variability is critical in describing regional hydroclimate, where snow ablation can influence streamflow, soil moisture and groundwater supplies. This study uses a gridded dataset of United States and Canadian snow ablation events derived from 1960 to 2009 surface observations to examine spatial and temporal variations of snow ablation frequency. Here, we show a relatively narrow band of peak ablation frequency seasonally advances and recedes over North America, forced by variations in snow depth and meteorological conditions suitable for ablation. Particularly in more moist regions away from the continent's interior, hydrologically relevant ablation events of at least 10.0 cm occur on an approximately yearly basis. Collectively, ablation events became significantly less frequent with time, where events specifically in the Appalachians and in Great Lakes regions declined by as much as 75% over the 50‐year period. Decreases in ablation frequency across the study region are primarily driven by significant decreases in snow cover, inhibiting the potential for ablation to occur due to a lack of sufficiently deep snowpacks. These results point to important snow cover related changes in the hydrologic cycle in a warming climate and highlight specific areas of interest where more localized analysis of ablation trends and forcing mechanisms would be appropriate.

Tracking mass removal of portable laser ablation sampling by its acoustic response

If the sample cannot be brought to the lab for sampling, then the sampling needs to be done at the sample location. The portable laser ablation (pLA) system is one of the candidates to address this challenge, as it is a powerful tool for field deployable sampling of solids with the benefits of laser based analysis methods. However, sampling in the field is not always as convenient as in a defined laboratory setting and requires a neat prior method development. In the field, the evaluation of the sampling performance is not straightforward with current hardware. During mass removal by (p)LA, an acoustic pressure wave is formed for every individual LA event. In order to track these signals, a directional microphone was integrated into the handheld pLA-module. This allowed the monitoring of the acoustic signal close to the ablation site to count and quantify LA events from each individual pulse. In order to monitor mass removal and acoustic response quasi-simultaneously, the pLA sampling device was coupled to an ICPMS via a gas-exchange device (GED). Performance was investigated using various samples. Discrepancies were observed between samples with low and high ablation thresholds. For samples with low ablation thresholds, e.g. metals, the acoustic signal was mainly influenced by the laser fluence at the ablation site and not by the amount of mass removal. Comparatively, when ablating samples with high ablation thresholds, such as glasses and minerals, these variations were less pronounced, resulting in the observation of a linear relationship. Consequently, this allows the use of the acoustic energy as a measure of the amount of mass removal. In summary, results show that this approach enables a straightforward way to track all actual ablation events during on-site sampling and allows an instant evaluation of the ablation performance, thereby reducing unsuccessful sampling sessions.

Three-dimensional (3D) imaging of lipids in skin tissues with infrared matrix-assisted laser desorption electrospray ionization (MALDESI) mass spectrometry.

Three-dimensional (3D) mass spectrometry imaging (MSI) has become a growing frontier as it has the potential to provide a 3D representation of analytes in a label-free, untargeted, and chemically specific manner. The most common 3D MSI is accomplished by the reconstruction of 2D MSI from serial cryosections; however, this presents significant challenges in image alignment and registration. An alternative method would be to sequentially image a sample by consecutive ablation events to create a 3D image. In this study, we describe the use of infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) in ablation-based 3D MSI for analyses of lipids within fresh frozen skin tissue. Depth resolution using different laser energy levels was explored with a confocal laser scanning microscope to establish the imaging parameters for skin. The lowest and highest laser energy level resulted in a depth resolution of 7μm and 18μm, respectively. A total of 594 lipids were putatively detected and detailed lipid profiles across different skin layers were revealed in a 56-layer 3D imaging experiment. Correlated with histological information, the skin structure was characterized with differential lipid distributions with a lateral resolution of 50μm and a z resolution of 7μm.

The changing nature of ablation-inducing synoptic weather types in the North American Great Lakes basin

The runoff generated by snow cover ablation dominates regional hydrology in the North American Great Lakes basin, while rapid events can represent a physical hazard due to flooding. In determining the likelihood and magnitude of an ablation event, both the presence of snow cover and the synoptic-scale atmospheric environment should be considered, where the atmospheric environment provides the meteorological characteristics and surface energy fluxes necessary for ablation. Pending snowpack availability, variations or changes in the frequency of ablation-inducing synoptic types, and/or varying suitability of meteorological characteristics for snowmelt, can alter the frequency of ablation events. In light of a changing global climate, it is unclear if and how ablation-inducing synoptic types in the Great Lakes basin have transformed in recent decades as from 1960 to 2009, the interannual frequency of snow cover ablation events in the Great Lakes basin has significantly decreased. This study uses synoptic classification as a mechanism for identifying ablation-inducing synoptic weather types and for determining if changes to the frequency and inherent meteorological characteristic of the type are occurring. For a majority of the ten most impactful ablation-inducing synoptic weather types examined, significant trends are noted in their interannual frequencies, which can be partially explained by variations and trends in the phases of common teleconnection indices, such as the North Atlantic and Arctic Oscillations. Collectively, inherent meteorological characteristics of particular weather types in the basin are becoming more suitable for ablation, with increases in surface air temperatures, more southerly wind flow, and less cloud cover, plus increases in liquid precipitation rates during rain-on-snow synoptic types. Independent of snow cover, atmospheric environments suitable for ablation are becoming more frequent and generally more favorable for ablation.

Impulse measurement of laser induced ablation in a vacuum

An impulse measurement system based on a simple pendulum is newly developed. The system has a resolution of 10-7 Ns for ablation events induced by a single laser at a pulse rate of 2 Hz or less. For ablation events at 10 Hz and above, the system can record the impulse as an average force. The impulse generated by a Nd:YAG pulse laser irradiating a 7075 aluminum alloy is investigated in vacuum. The impulse arises at 3 J/cm2 and the momentum coupling factor, Cm, plateaus at approximately 20 μNs/J over a range of 5 to 50 J/cm2 without producing a plasma shielding effect. Cm is characterized by only fluence independent of pulse width in the range of 10 to 20 ns. This result indicates that it should be feasible to deorbit a 150 kg abandoned satellite at an altitude of 1200 km using a chaser satellite equipped with a 100 W laser.