Damage Tracks Research Articles

Complications of RFA for Thyroid Nodules: Prevention and Management

This review will summarize the various complications of RFA for thyroid nodules as well as preventative and management strategies that can be used when faced with these adverse events. Although widely perceived to be less invasive and a potentially safer option than surgery, a broad spectrum of complications have been reported in recent years, including nerve damage, nodule rupture, permanent hypothyroidism, and needle tracking seeding. Complications occur at a rate ranging from 0.0–16.7%. Understanding the complications that arise during treatment is essential in conducting safe and effective ablation therapy. Radiofrequency ablation (RFA) has become an increasingly popular alternative to surgery for thyroid nodules. RFA has been consistently shown to be safe and effective for treatment. While complications can occur, they are seldom life-threatening. Understanding the minor and major complications that arise during treatment is essential in conducting safe and effective ablation therapy.

\u03b1-Particle-induced DNA damage tracks in peripheral blood mononuclear cells of [223Ra]RaCl2-treated prostate cancer patients

PurposeOne therapy option for prostate cancer patients with bone metastases is the use of [223Ra]RaCl2. The α-emitter 223Ra creates DNA damage tracks along α-particle trajectories (α-tracks) in exposed cells that can be revealed by immunofluorescent staining of γ-H2AX+53BP1 DNA double-strand break markers. We investigated the time- and absorbed dose-dependency of the number of α-tracks in peripheral blood mononuclear cells (PBMCs) of patients undergoing their first therapy with [223Ra]RaCl2.MethodsMultiple blood samples from nine prostate cancer patients were collected before and after administration of [223Ra]RaCl2, up to 4 weeks after treatment. γ-H2AX- and 53BP1-positive α-tracks were microscopically quantified in isolated and immuno-stained PBMCs.ResultsThe absorbed doses to the blood were less than 6 mGy up to 4 h after administration and maximally 16 mGy in total. Up to 4 h after administration, the α-track frequency was significantly increased relative to baseline and correlated with the absorbed dose to the blood in the dose range < 3 mGy. In most of the late samples (24 h – 4 weeks after administration), the α-track frequency remained elevated.ConclusionThe γ-H2AX+53BP1 assay is a potent method for detection of α-particle-induced DNA damages during treatment with or after accidental incorporation of radionuclides even at low absorbed doses. It may serve as a biomarker discriminating α- from β-emitters based on damage geometry.

Anticipating Deviant Tornado Motion Using a Simple Hodograph Technique

AbstractThe paths of tornadoes have long been a subject of fascination since the meticulously drawn damage tracks by Dr. Tetsuya Theodore “Ted” Fujita. Though uncommon, some tornadoes have been noted to take sudden left turns from their previous path. This has the potential to present an extreme challenge to warning lead time, and the spread of timely, accurate information to broadcasters and emergency managers. While a few hypotheses exist as to why tornadoes deviate, none have been tested for their potential use in operational forecasting and nowcasting. As a result, such deviations go largely unanticipated by forecasters. A sample of 102 leftward deviant tornadic low-level mesocyclones was tracked via WSR-88D and assessed for their potential predictability. A simple hodograph technique is presented that shows promising skill in predicting the motion of deviant tornadoes, which, upon “occlusion,” detach from the parent storm’s updraft centroid and advect leftward or rearward by the low-level wind. This metric, a vector average of the parent storm motion and the mean wind in the lowest half-kilometer, proves effective at anticipating deviant tornado motion with a median error of less than 6 kt (1 kt ≈ 0.51 m s−1). With over 25% of analyzed low-level mesocyclones deviating completely out of the tornado warning polygon issued by their respective National Weather Service Weather Forecast Office, the adoption of this new technique could improve warning performance. Furthermore, with over 35% of tornadoes becoming “deviant” almost immediately upon formation, the ability to anticipate such events may inspire a new paradigm for tornado warnings that, when covering unpredictable behavior, are proactive instead of reactive.

Reveal of Internal, Early-Load Interfacial Debonding on Cement Textile-Reinforced Sandwich Insulated Panels

Internal interfacial debonding (IID) phenomena on sandwich façade insulated panels are detected and tracked by acoustic emission (AE). The panels are made of a thin and lightweight cementitious composite skin. In the lab, the panels are tested under incremental bending simulating service loads (i.e., wind). Local (up to 150 mm wide) skin-core detachments are reported in the early loading stage (at 5% of ultimate load) and are extensively investigated in this study, since IID can detrimentally affect the long-term durability of the structural element. A sudden rise in the AE hits rate and a shift in the wave features (i.e., absolute energy, amplitude, rise time) trends indicate the debonding onset. AE source localization, validated by digital image correlation (DIC) principal strains and out-of-plane full-field displacement mapping, proves that early debonding occurs instantly and leads to the onset of cracks in the cementitious skin. At higher load levels, cracking is accompanied by local debonding phenomena, as proven by RA value increases and average frequency drops, a result that extends the state-of-the-art in the fracture assessment of concrete structures (Rilem Technical Committee 212-ACD). Point (LVDT) and full-field (AE/DIC) measurements highlight the need for a continuous and full-field monitoring methodology in order to pinpoint the debonded zones, with the DIC technique accurately reporting surface phenomena while AE offers in-volume damage tracking.

Measuring Changes in the Atmospheric Neutrino Rate over Gigayear Timescales.

Measuring the cosmic ray flux over timescales comparable to the age of the Solar System, ∼4.5 Gyr, could provide a new window on the history of the Earth, the Solar System, and even our Galaxy. We present a technique to indirectly measure the rate of cosmic rays as a function of time using the imprints of atmospheric neutrinos in "paleo-detectors," natural minerals that record damage tracks from nuclear recoils. Minerals commonly found on Earth are ≲1 Gyr old, providing the ability to look back across cosmic ray history on timescales of the same order as the age of the Solar System. Given a collection of differently aged samples dated with reasonable accuracy, this technique is particularly well-suited to measuring historical changes in the cosmic ray flux at Earth and is broadly applicable in astrophysics and geophysics.

Prognostic-oriented Fuel Cell Catalyst Aging Modeling and Its Application to Health-Monitoring and Prognostics of a PEM Fuel Cell

Today, poor long-term performance and durability combined with high production and maintenance costs remain the main obstacles for the commercialization of the polymer electrolyte membrane (PEM) fuel cells (PEMFCs). While on-line diagnosis and operating condition optimization play an important role in addressing the durability issue of the fuel cell, health-monitoring and prognosis (or PHM) techniques are of equally great significance in terms of scheduling condition-based maintenance (CBM) to minimize repair and maintenance costs, the associated operational disruptions, and also the risk of unscheduled downtime for the fuel cell systems.The two essential components of a PHM scheme for a general engineering system are 1) an accurate aging model that is capable of capturing the system’s gradual health deterioration, and 2) an algorithm for damage estimation and prognostics. In this paper, a physics-based, prognostic-oriented fuel cell catalyst degradation model is developed to characterize the relationship between the operating conditions and the degradation rate of the electro-chemical surface area (ECSA). The model complexity is kept minimal for on-line prognostic purpose. An unscented Kalman filter (UKF) approach is then proposed for the purpose of damage tracking and remaining useful life prediction of a PEMFC.

Uso de sensoriamento remoto via satélite na identificação de rastros de destruição por tornados em um evento de tempo severo no Rio Grande do Sul

The number of tornado reports in Brazil has increased in recent years; nevertheless, it is likely that many occurrences over uninhabited areas and/or during night time hours remain unconfirmed, especially in a country devoid of official surveys of damage caused by intense winds. This work follows previous initiatives addressing the employment of remote sensing via satellite to identify damage paths associated with tornadoes. The nocturnal event analyzed in this study took place in north-northeast Rio Grande do Sul state from the night hours of 7 June 2017 into early morning hours of the following day, and represents an example of the characterization of significant damage caused by tornadoes despite the lack of visual confirmation of the phenomenon. Images produced by low-orbit environmental satellites of the Landsat and Sentinel series are analyzed, as well as imagery made available by the commercial-purpose environmental satellites that comprise the data base of Google Earth software. To aid in the identification of damage inflicted to dense vegetation, the web tools Global Florest Change and Global Florest Watch, which employ objective methods to detect abrupt modifications in the vegetation cover, are also utilized. Based on these products, it was possible to identify seven tornado damage tracks for the nocturnal event of June 2017, ratifying the value added by remote sensing products in the confirmation of tornadic episodes.

Reanalysing strong-convective wind damage paths using high-resolution aerial images

High-resolution aerial imagery may provide very detailed information about strong-convective wind events, which can be very useful to enhance and make more robust severe weather databases. Through an aerial analysis, unknown affected areas can be unveiled, large damaged zones or complex terrain events can be mapped, and in situ damage surveys can be completed. Comparing aerial orthophotographs or high-resolution satellite imagery taken before and after the event, damage to forest associated with EF1 + intensities rated with the Enhanced Fujita scale is easily observable. It is also possible to detect repaired parts on some types of roofs and buildings due to the occurrence of weak events and major damage on human-made structures in case of significant episodes. To illustrate the added value of using orthophotographs in forensic damage survey analysis, the 2 November 2008 strong-convective wind event in Catalonia (NE Iberian Peninsula) is revisited. Confirming previous studies, two different damage swaths, associated with the passage of two supercells during the early morning, are clearly identified in high-resolution aerial images. The additional information provided by orthophotograph analysis allowed extending the two damage paths and increasing the damage intensity of the event. It is concluded that both damage tracks are related to tornadoes, which are rated as an EF2 and an EF3, the second being the strongest tornado ever registered in Catalonia, one of the most tornado-prone regions of southern Europe.

Two-axle test vehicle for damage detection for railway tracks modeled as simply supported beams with elastic foundation

For damage detection of railway tracks, a two-axle test vehicle is better than a single-axle vehicle due to its capability of self standing and stability. This paper presents a new, comprehensive theoretical framework for a two-axle test vehicle moving over railway tracks modeled as a simply supported beam with elastic foundation. Firstly, closed-form solutions for both the vehicle and rail responses of the system were derived, along with those for the two contact points by a back calculation procedure. Secondly, the driving component of the contact-point response was processed by the Hilbert transform to yield the Instantaneous Amplitude Squared (IAS) for damage detection. Then, the efficacy of the proposed technique was numerically validated by the Finite Element Method (FEM). Particularly, the sensitivity of the proposed technique was investigated against various factors, including the damage severity, multi damages, vehicle speed, track unevenness, track damping, and measurement noise. The result shows that the IAS of the driving component of the contact point response of the railway track is a good damage indicator in that it is of low frequencies and narrow band, while its modal amplitude is sensitive to the stiffness loss in rail supports.

Paleodetectors for Galactic supernova neutrinos

Paleo-detectors are a proposed experimental technique in which one would search for traces of recoiling nuclei in ancient minerals. Natural minerals on Earth are as old as $\mathcal{O}(1)\,$Gyr and, in many minerals, the damage tracks left by recoiling nuclei are also preserved for timescales long compared to 1 Gyr once created. Thus, even reading out relatively small target samples of order 100 g, paleo-detectors would allow one to search for very rare events thanks to the large exposure, $\varepsilon \sim 100\,{\rm g}\,{\rm Gyr} = 10^5\,{\rm t}\,{\rm yr}$. Here, we explore the potential of paleo-detectors to measure nuclear recoils induced by neutrinos from galactic core collapse supernovae. We find that they would not only allow for a direct measurement of the average core collapse supernova rate in the Milky Way, but would also contain information about the time-dependence of the local supernova rate over the past $\sim$1 Gyr. Since the supernova rate is thought to be directly proportional to the star formation rate, such a measurement would provide a determination of the local star formation history. We investigate the sensitivity of paleo-detectors to both a smooth time evolution and an enhancement of the core collapse supernova rate on relatively short timescales, as would be expected for a starburst period in the local group.

Spatio-temporal characterization of slope damage: insights from the Ten Mile Slide, British Columbia, Canada

The deformation and failure of slopes is associated with the formation of geomorphic features reflecting “external slope damage.” Characterizing the spatial and temporal distribution of slope damage is beneficial to understanding the mechanisms and processes underlying slope instability. To date, characterization of slope damage has predominantly been performed using qualitative approaches. In this paper, a new workflow for the quantitative, spatio-temporal characterization of the external slope damage is described and applied to the investigation of the Ten Mile Slide, an active landslide located in southern British Columbia. Since 2006, monitoring activity at the site has included periodic repeat airborne laser scanning (ALS) surveys, which have allowed the creation of a high-detail, three-dimensional database showing the progressive deformation and retrogression of the slide. External slope damage features are manually mapped in the ALS datasets, and slope damage intensity is then computed and displayed on thematic maps. The proposed workflow introduces important new slope damage measures including External Discrete Slope Damage Feature maps (EDSDF), External Slope Damage Intensity Cell (ESDICe) maps, External Slope Damage Intensity Contour (ESDICo) maps and slope damage intensity spatio-temporal plots. The new spatio-temporal damage measures are used to create damage index tables and track changes in slope damage intensity with time at any point within the slide area. The spatio-temporal analysis shows that the distribution of external slope damage features is not homogeneous across the Ten Mile Slide area. In particular, the spatio-temporal damage methodology outlines higher accumulation slope damage rates along the eastern boundary of the slide area, due to the presence of a stream incision that provides kinematic freedom and allows the lateral deformation of the slide and the formation of tensile cracking. The proposed approach in this thesis allows comprehensive, quantitative, and repeatable damage analysis to be undertaken, providing a robust method for characterizing the geomorphic evolution of slopes from a damage perspective. This research methodology provides engineers and geoscientists with a valuable tool for planning subsequent slope investigation and optimizing new or existing monitoring and early-warning systems.

Data-driven damage tracking and hysteresis evaluation of earthquake-excited structures with test validation

A data-driven damage tracking and hysteresis evaluation method for earthquake-excited structures that adopts the model-reference concept is presented in this paper. A series of target substructures with local interstory hysteresis is first decentralized from the global structure system adopting the Rayleigh damping model. A linear reference model, designed to be identified from nondestructive seismic events, is used to represent the desired healthy behaviors. The tracking error of structural responses with a substructure-level loading reconstruction is subsequently introduced to quantify the potential behavior deviation during a disastrous earthquake. Such a structural behavior deviation, in terms of a normalized form, has been proposed in a novel data-driven damage model; accordingly, a logistic framework has been presented for the quantification of structural damage of interests. Two illustrative examples, including a numerical simulation of a three degree-of-freedom degradation model and an experimental investigation of a large-scale reinforced concrete frame through a shaking table test, have been employed. Comprehensive results and detailed discussion are presented to illustrate the damage tracking and quantification performances of the proposed data-driven evaluation method.

Using Hybrid Filter-Wrapper Feature Selection With Multi-Objective Improved-Salp Optimization for Crack Severity Recognition

The emerging technology of Structural Health Monitoring (SHM) paved the way for spotting and continuous tracking of structural damage. One of the major defects in historical structures is cracking, which represents an indicator of potential structural deterioration according to its severity. This paper presents a novel crack severity recognition system using a hybrid filter-wrapper with multi-objective optimization feature selection method. The proposed approach comprises two main components, namely, (1) feature extraction based on hand-crafted feature engineering and CNN-based deep feature learning and (2) feature selection using hybrid filter-wrapper with a multi-objective improved salp swarm optimization. The proposed approach is trained and validated by utilizing 10 representative UCI datasets and 4 datasets of crack images. The obtained experimental results show that the proposed system enhances the performance of crack severity recognition with ≈ 37% and ≈ 31% increase in recognition average accuracy and F-measure, respectively. Also, a reduction rate of ≈ 67% is achieved in the extracted feature set with all the tested datasets compared to the conventional classification approaches using the whole set of features. Moreover, the proposed approach outperforms other approaches with classical feature selection methods in terms of feature reduction rate and computational time. It is noticed that using VGG16 learned features outperforms using the fused hand-crafted features by 17.7%, 15.9%, and 23.5% for fine, moderate, and severe crack recognition, respectively. The significance of this paper is to investigate and highlight the impact of applying multi-feature dimensionality reduction through adopting hybrid filter-wrapper with multi-objective optimization methods for feature selection considering the case study of crack severity recognition for SHM.

Data Compression Approach for Long-Term Monitoring of Pavement Structures

Pavement structures are designed to withstand continuous damage during their design life. Damage starts as soon as the pavement is open to traffic and increases with time. If maintenance activities are not considered in the initial design or considered but not applied during the service life, damage will grow to a point where rehabilitation may be the only and most expensive option left. In order to monitor the evolution of damage and its severity in pavement structures, a novel data compression approach based on cumulative measurements from a piezoelectric sensor is presented in this paper. Specifically, the piezoelectric sensor uses a thin film of polyvinylidene fluoride to sense the energy produced by the micro deformation generated due to the application of traffic loads. Epoxy solution has been used to encapsulate the membrane providing hardness and flexibility to withstand the high-loads and the high-temperatures during construction of the asphalt layer. The piezoelectric sensors have been exposed to three months of loading (approximately 1.0 million loads of 65 kN) at the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) fatigue carrousel. Notably, the sensors survived the construction and testing. Reference measurements were made with a commercial conventional strain gauge specifically designed for measurements in hot mix asphalt layers. Results from the carrousel successfully demonstrate that the novel approach can be considered as a good indicator of damage progression, thus alleviating the need to measure strains in pavement for the purpose of damage tracking.

Nanostructure of Clustered DNA Damage in Leukocytes after In-Solution Irradiation with the Alpha Emitter Ra-223.

Background: Cancer patients are increasingly treated with alpha-particle-emitting radiopharmaceuticals. At the subcellular level, alpha particles induce densely spaced ionizations and molecular damage. Induction of DNA lesions, especially clustered DNA double-strand breaks (DSBs), threatens a cell’s survival. Currently, it is under debate to what extent the spatial topology of the damaged chromatin regions and the repair protein arrangements are contributing. Methods: Super-resolution light microscopy (SMLM) in combination with cluster analysis of single molecule signal-point density regions of DSB repair markers was applied to investigate the nano-structure of DNA damage foci tracks of Ra-223 in-solution irradiated leukocytes. Results: Alpha-damaged chromatin tracks were efficiently outlined by γ-H2AX that formed large (super) foci composed of numerous 60–80 nm-sized nano-foci. Alpha damage tracks contained 60–70% of all γ-H2AX point signals in a nucleus, while less than 30% of 53BP1, MRE11 or p-ATM signals were located inside γ-H2AX damage tracks. MRE11 and p-ATM protein fluorescent tags formed focal nano-clusters of about 20 nm peak size. There were, on average, 12 (±9) MRE11 nanoclusters in a typical γ-H2AX-marked alpha track, suggesting a minimal number of MRE11-processed DSBs per track. Our SMLM data suggest regularly arranged nano-structures during DNA repair in the damaged chromatin domain.

Energy dependent structure of Xe ion tracks in YBCO and the effect on the superconductive properties in magnetic fields

The morphology and structure of damaged regions (tracks) produced by swift heavy 167, 77, and 46 MeV 132Xe23+ ions in YBCO-based second generation industrial high temperature superconductors wires (2G HTS) were studied using transmission electron microscopy. It was shown that ions produce tracks aligned along the ion trajectory but of morphology depending on their energy: continuous, nearly continuous, or discontinuous tracks like prolate ellipsoids of 10–15 nm in length and spheroids of 5 nm in diameter. The damaged regions of about 5 nm in diameter contain an amorphous material with a lower density compared to the pristine YBCO. The material density drops from 6300 kg m−3 for YBCO matrix to 3600 kg m−3 inside the tracks. Barium enrichment was found in the vicinity of the track at a distance of about 10 nm from the center of the defect. Ion damage tracks with different morphologies showed different effectivenesses as pinning centers. Tracks composed of discontinuous pinning centers—spheroids of about 5 nm in diameter—bring the best enhancement of the critical current density. It occurs for the lowest ion energy (46 MeV) in the range of energy loss of 8.9 keV/nm–4.7 keV/nm for Xe ions. The samples showed highest critical current densities of 56 MA/cm2 (4.2 K) and 3 MA/cm2 (77 K) in self-field, while in magnetic fields of 8 T, the values of 17 MA/cm2 (4.2 K) and 1.6 MA/cm2 (77 K) were achieved. The reduction of the superconducting volume corresponding to the amorphous radiation defects did not exceed 4% from the total sample volume.

P6249Markers of early myocardial damage in steinert's disease

Abstract Introduction Myotonic dystrophy type 1 (DM 1), also known as Steinert's disease (SD), is the most common muscular dystrophy in adults. It is characterized by multisystemic involvement and the cardiac affectation is the second leading cause of death after the respiratory one. Purpose The objective of our work was to study the cardiac involvement by transthoracic echocardiography (TTE) including systolic function, diastolic function and myocardial deformation with global longitudinal strain (GLS) by speckle tracking and trough biomarkers of myocardial damage with high-sensitive cardiac troponin T (hs-cTnT) and NT-proBNP. Methods 24 patients affected by SD were included. The TTE machine used has software to perform GLS with reference values: −20±2%. The normal values of hs-cTnT and NT-proBNP of our central laboratory are: &lt;14 ng/L and 0–250 pg/ml, respectively. Results The mean age of patients was 52,08±12,14 years and the average age of diagnosis was 31,42 years. There was no gender predilection (12 women, 12 men). In the TTE 55% of patients had a GLS &lt;−18% with a global average of −17,72±4,02%. The 50% of patients with LVEF &gt;50% had a GLS &lt;−18% and the 27,77% had a GLS between −18 and −20%. The diastolic dysfunction assessed by pulsed wave doppler and tissue doppler imaging was present in 26.82%. The 95,83% of the patients had levels of hs-cTnT≥14 ng/L with median of 34,93 ng/L (minimum 3,96 and maximum 429), however only 30,4% of these had values of NT-proBNP above 250 pg/ml with a median of 71,83 pg/ml (minimum 9,37 and maximum 8771). Conclusions According to our experience GLS and hs-cTnT could be markers of early myocardial damage in patients with SD. We therefore need to develop protocols for the follow-up including these markers in the usual cardiac assessment.

Damage localization in irregular shape structures using intelligent FE model updating approach with a new hybrid objective function and social swarm algorithm

Health monitoring of structures and damage diagnosis are important research disciplines under investigation worldwide. Soft computing techniques are usually used to solve the uncertain complex inverse problem of revealing structural damage. In the current research, FE model updating (FEMU) paradigm is embraced for solving the damage tracking problem in three dimensional irregular shape structures. By taking into account the complexity of problem, the pivotal point is to efficiently educe damage through well-evolved objective function. Therefore, a novel objective function merging the modal characteristics of modal strain energy (MSTEN) and mode shape curvature (MSC) is established. Posteriorly, to solve the FEMU problem, a hybrid algorithm combining the particle swarm optimization with a new social version of the sine–cosine optimization algorithm (SPSOSCA) is proposed. The SPSOSCA is considered to take advantage of two enhanced search mechanisms to overcome the overall problem complexity. The proposed paradigm is evaluated using many damage scenarios even under noise conditions and the total outcome reveals outstanding performance with fair computational time.

LC8/DYNLL1 is a 53BP1 effector and regulates checkpoint activation.

The tumor suppressor protein 53BP1 plays key roles in response to DNA double-strand breaks (DSBs) by serving as a master scaffold at the damaged chromatin. Current evidence indicates that 53BP1 assembles a cohort of DNA damage response (DDR) factors to distinctly execute its repertoire of DSB responses, including checkpoint activation and non-homologous end joining (NHEJ) repair. Here, we have uncovered LC8 (a.k.a. DYNLL1) as an important 53BP1 effector. We found that LC8 accumulates at laser-induced DNA damage tracks in a 53BP1-dependent manner and requires the canonical H2AX-MDC1-RNF8-RNF168 signal transduction cascade. Accordingly, genetic inactivation of LC8 or its interaction with 53BP1 resulted in checkpoint defects. Importantly, loss of LC8 alleviated the hypersensitivity of BRCA1-depleted cells to ionizing radiation and PARP inhibition, highlighting the 53BP1-LC8 module in counteracting BRCA1-dependent functions in the DDR. Together, these data establish LC8 as an important mediator of a subset of 53BP1-dependent DSB responses.

Ionization behavior and dynamics of picosecond laser filamentation in sapphire

Currently, laser-induced structural modifications in optical materials have been an active field of research. In this paper, we reported structural modifications in the bulk of sapphire due to picosecond (ps) laser filamentation and analyzed the ionization dynamics of the filamentation. Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material. The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track. By increasing laser energy, the length of the damage and filamentary track appeared to increase. In addition, the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations, but no increase in the filamentary zone diameter was observed with increasing laser energy.