Comprehensive Identification and Ubiquitous Occurrence of Eight Classes of Rubber-Derived Vulcanization Accelerators in Urban Dusts.

Vulcanization accelerators (VAs) serve as crucial additives in synthetic rubber on a global scale. Despite their widespread use, the environmental presence, distribution, and associated exposure risks of VAs remain poorly understood. This study compiled a target list and conducted a screening for eight classes encompassing 42 VAs in diverse urban dust samples from South China. A total of 40 of the 42 target VAs were detectable across all four studied regions, among which 30 were identified for the first time in the environment. Among the eight structure-classified VA classes, xanthates exhibited the highest concentrations (median: 3810-81,300 ng/g), followed by thiazoles, guanidines, sulfenamides, dithiocarbamates, thiurams, thioureas, and others. The median total concentrations of all target VAs (∑VAs) were determined to be 5060 ng/g in road dust, 5730 ng/g in parking lot dust, 29,200 ng/g in vehicle repair plant dust, and 84,300 ng/g in household dust, indicating the widespread presence of numerous rubber-derived VAs in various urban environments. This study marked the first systematic effort to identify a wide range of emerging rubber-derived VAs prevalent in urban environments. The findings call for increased attention to these widely utilized but less well-evaluated chemicals in future research and environmental management efforts.

Contact allergy to rubber accelerators in consecutively patch tested Danish eczema patients: A retrospective observational study from 1990 to 2019.

BACKGROUND: Rubber accelerators are used in the production of rubber gloves and may cause contact allergy. OBJECTIVES: To estimate long-term trend and prevalence of contact allergy to rubber accelerators for a 30-year period in Denmark, high-risk occupations, and exposures. METHODS: Data from all patients with contact dermatitis consecutively patch tested at the department of Skin and Allergy Gentofte hospital with the rubber accelerators from the European baseline series (EBS) from 1990 to 2019, were analysed. Further, patients under suspicion of rubber accelerator contact allergy were additionally patch-tested with rubber accelerators from the specialised rubber series from 2005 to 2019 and these were additional extracted. RESULTS: The overall prevalence of contact allergy to one or more of the rubber accelerators from the EBS series was 2.7% with a significant decline in the first 12-years, followed by a stable frequency in the past 18-years. Associations with occupational contact dermatitis, hand dermatitis, and leg/foot dermatitis were found. Wet-work occupations were most often affected and gloves the most frequent exposure. CONCLUSIONS: Contact allergy to one or more of the rubber accelerators from the EBS is frequent and has been unchanged for several decades, which calls for prevention.

Cross-reactivity between thiuram disulfides and dithiocarbamates. A study of TETD and ZDEC using mouse models.

BACKGROUND: Rubber accelerators are used in the vulcanization of rubber. However, rubber accelerators for example tetraethylthiuram disulfide (TETD) and zinc diethyldithiocarbamate (ZDEC) may cause contact allergy. Concomitant reactions between ZDEC and TETD have been observed in patients which could be explained by co- or cross-reactivity. OBJECTIVES: To investigate cross-reactivity between TETD and ZDEC and vice versa. METHODS: Groups of mice were sensitized with TETD or ZDEC based on reported EC3-values. Proliferation of lymphocytes were measured on day 5. To test cross-reactivity, mice were sensitized and challenged 3 weeks later with TETD or ZDEC. The inflammatory response was measured by changes in ear thickness and the proliferative response in CD4+ and CD8+ T cells in the submandibular and cervical draining lymph nodes. RESULTS: Sensitization of mice with doses of ZDEC 3%, TETD 5.6% or TETD 16.2% induced significant increased ear thickness and proliferation of CD4+ and CD8+ T cells. Challenge with ZDEC or TETD in these groups induced significant increased ear thickness. Challenge with ZDEC in mice sensitized to TETD 5.6% or TETD 16.2% induced significant increased proliferation of CD4+ and CD8+ T cells. CONCLUSIONS: We show cross-reactivity between TETD and ZDEC. Patients sensitized to TETD or ZDEC should avoid exposure to both ZDEC and TETD.

Contents of sensitising rubber accelerators in disposable rubber gloves: A Copenhagen market survey.

BACKGROUND: Rubber gloves contain rubber accelerators that may cause contact allergy. The content of sensitising rubber accelerators in contemporary rubber gloves is not well known. OBJECTIVES: Identify and quantify the content of rubber accelerators in disposable rubber gloves. METHODS: Fifty-one gloves of 49 different brands were collected. Forty-eight of the gloves were disposable and three re-usable. The gloves were analysed for their content of sensitising rubber accelerators, that is, zinc dithiocarbamates, thiurams, thiazoles/benzothiazoles, diphenylguanidine, and thioureas by high-performance liquid chromatography. RESULTS: Rubber accelerators were identified in 43/48 (90%) of the disposable gloves. In total, 39 gloves contained zinc dibutyldithiocarbamate (ZDBC) (0.18-1.96 mg/g), 34 zinc diethyldithiocarbamate (ZDEC) (0.032-2.78 mg/g), three zinc dibenzyldithiocarbamate (0.65-1.4 mg/g), one zinc dimethyldithiocarbamate (0.23 mg/g), and one 1,3-diphenylguanidine (0.21 mg/g). 2-cyanoethyl dimethyldithiocarbamate (CEDMC) was identified in three gloves (<0.052 mg/g). The one glove labelled as accelerator free contained ZDBC (1.07 mg/g). Only few glove packages had the specific content of rubber accelerators labelled. CONCLUSIONS: The most frequent rubber accelerators in rubber gloves are ZDEC and ZDBC. Accelerator-free gloves may contain rubber accelerators. Full labelling of rubber gloves is needed and producers should be sure not to falsely claim that the rubber gloves are free of rubber accelerators.

Sub-THz Characterization of Technical Surfaces for Particle Accelerator Vacuum Chambers.

Coatings play a crucial role in the functionality of vacuum chambers in particle accelerators, serving a dual goal by efficiently facilitating pumping and mitigating electron cloud effects. However, their impact on the surface impedance of the chamber walls raises concerns, potentially affecting the machine performance and imposing limitations on achievable energies and currents. Therefore, an electromagnetic characterization is essential for a comprehensive study of accelerator structures, particularly in the context of the next-generation machines where the demand for extremely short particle bunches accentuates the importance of evaluating material responses in the very-high-frequency region. We present a technique for probing the sub-THz response of coating materials by measuring pulsed signals passing through a specifically designed waveguide, in which is placed a slab with the deposited material under test. The proposed methodology allows for a comprehensive exploration of the electromagnetic properties of the most used technical surfaces (substrate plus coatings) in accelerators under realistic conditions, providing valuable insights into their behavior in the sub-THz frequency range. The experimental data of three different Non-Evaporable Getter coating samples, prepared on a copper substrate at the CERN deposition facilities under different sputtering conditions, are discussed. The findings contribute to a deeper understanding of the complex interactions between coatings and accelerator structures, with the aim of optimizing performance and efficiency in the evolving landscape of particle acceleration technologies. The limitations and advantages of the technique are also reported.

Pulsed-Mode Magnetic Field Measurements with a Single Stretched Wire System.

In synchrotrons, accurate knowledge of the magnetic field generated by bending dipole magnets is essential to ensure beam stability. Measurement campaigns are necessary to characterize the field. The choice of the measurement method for such campaigns is determined by the combination of magnet dimensions and operating conditions and typically require a trade-off between accuracy and versatility. The single stretched wire (SSW) is a well-known, polyvalent method to measure the integral field of magnets having a wide range of geometries. It, however, requires steady-state excitation. This work presents a novel implementation of this method called pulsed SSW, which allows the system to measure rapidly time-varying magnetic fields, as is often needed, to save power or gain beam time. We first introduce the measurement principle of the pulsed SSW, followed by a combined strategy to calculate the absolute magnetic field by incorporating the classic DC SSW method. Using a bending magnet from the Proton Synchrotron Booster located at the European Organization for Nuclear Research as a case study, we validate the pulsed SSW method and compare its dynamic measurement capabilities to a fixed induction coil, showing thereby how the coil calibration must be adjusted according to the field level. Finally, we assess the method's measurement accuracy using the standard SSW as a reference and present an analysis of the primary noise contributors.

Efficient FPGA Implementation of Convolutional Neural Networks and Long Short-Term Memory for Radar Emitter Signal Recognition.

In recent years, radar emitter signal recognition has enjoyed a wide range of applications in electronic support measure systems and communication security. More and more deep learning algorithms have been used to improve the recognition accuracy of radar emitter signals. However, complex deep learning algorithms and data preprocessing operations have a huge demand for computing power, which cannot meet the requirements of low power consumption and high real-time processing scenarios. Therefore, many research works have remained in the experimental stage and cannot be actually implemented. To tackle this problem, this paper proposes a resource reuse computing acceleration platform based on field programmable gate arrays (FPGA), and implements a one-dimensional (1D) convolutional neural network (CNN) and long short-term memory (LSTM) neural network (NN) model for radar emitter signal recognition, directly targeting the intermediate frequency (IF) data of radar emitter signal for classification and recognition. The implementation of the 1D-CNN-LSTM neural network on FPGA is realized by multiplexing the same systolic array to accomplish the parallel acceleration of 1D convolution and matrix vector multiplication operations. We implemented our network on Xilinx XCKU040 to evaluate the effectiveness of our proposed solution. Our experiments show that the system can achieve 7.34 giga operations per second (GOPS) data throughput with only 5.022 W power consumption when the radar emitter signal recognition rate is 96.53%, which greatly improves the energy efficiency ratio and real-time performance of the radar emitter recognition system.

Identifying potential catalysts to accelerate the achievement of Sustainable Development Goals (SDGs) among adolescents living in Nigeria.

Investing in adolescents in Africa holds great promise for the development of the continent. The steps involved in identifying factors linked to interventions that may accelerate the attainment of multiple SDGs for adolescents in Nigeria are described. Data from a survey to investigate the well-being of 1800 adolescents aged 10-19 years in Southwest Nigeria was analysed. A four-step process was employed: 1) Mapping of variables deemed as suitable proxies for SDG targets; 2) Mapping hypothesised protective factors (accelerators) from the study instruments. Consequently, SDG targets related to elimination of hunger, good health, gender equality and peace; and seven accelerators (safe schools, parenting support, good mental health, no survival work, food security, stable childhood, and regular physical activity) were identified; 3) evaluating associations using bivariate analysis and multivariable logistic regression, 4) calculating adjusted probabilities. The mean age of the adolescents was 15.02 ± 2.27 years (48.6% female). Good mental health, not doing survival work, safe schools, stable childhood and parental support were significantly associated with at least two SDG targets. For example, food security was significantly associated with the highest number of SDG outcomes: one SDG target related to child survival (no substance use: x2 = 3.39, p = <0.001); three SDG targets related to educational outcomes (school progression: x2 = 5.68, p = 0.017, ability to concentrate in school: x2 = 26.92, p = <0.001, and school attendance: x2 = 25.89, p = <0.001); and four SDG targets related to child protection (no risky sexual behaviours: x2 = 16.14, p = <0.001, no perpetration of violence: x2 = 15.74, p = <0.001, no community violence: x2 = 39.06, p =<0.001, and no sexual abuse: x2 = 7.66, p = 0.006). Interventions centred around good mental health, not doing survival work, safe schools, small family size, stable childhood and parental support are potential accelerators for the attainment of SDG outcomes by adolescents living in Nigeria.

Assessment of prostate cancer radiotherapy using three-dimensional treatment planning technique.

OBJECTIVE: To assess the available commercial treatment planning system using three-dimensional conformal radiation therapy with respect to treatment for prostate cancer patients. METHODS: This is a cross-sectional study was conducted from June 2021 to February 2022 at the Baghdad Centre for Radiation Therapy and Nuclear Medicine, Baghdad, Iraq, and comprised patients with prostate cancer who were treated with 6MV or 10MV energy using three-dimensional conformal radiation therapy technique, and irradiated using a linear accelerator. The patents were divided into three treatment phases. The prescribed dose in Phase I was 5000 centigrade, in Phase II it was 1800 centigrade, and in Phase III it was 600 centigrade. The number of beams used was 5 and 7. Data was analysed using SPSS 24. RESULTS: Out of 35 patients, 10 (28.6%) in phase I, 15 (42.8%) in phase II, and 10 (28.6%) in phase III. The PTV dose of 5 and 7 beams 6MV energy at the centre was higher than at 1mm, 2mm, and 3mm p values = (0.351, 0.013*, 0.076, 0.295), respectively. Dose to the rectum comparing 6MV and 10MV for beams 5, and 7. The dose to the rectum on phase one at 6MV and 10MV was similar for 5 beams (p=0.611) and 7 beams (p=0.778). A significant difference was seen for 7 beams (p-value=0.008). Phase three showed significant variations in rectum dose at 6 MV and 10MV for 5 beams (p=0.0004). For bladder, a significant difference observed between the energies for 5 beams on phase one and three (p-value=<0.00001*, 0.002*), while at 7 beams only phase 3 were significant (p-value=0.041*). CONCLUSIONS: The three-dimensional conformal radiation therapy plan with 10MV energy and a higher number of beams gave a higher coverage of dose for prostate tumours and was found to be a safe dose for the rectum and bladder.

Ubiquity of Amino Accelerators and Antioxidants in Road Dust from Multiple Land Types: Targeted and Nontargeted Analysis.

Amino accelerators and antioxidants (AAL/Os), as well as their degradation derivatives, are industrial additives of emerging concern due to their massive production and use (particularly in rubber tires), pervasiveness in the environment, and documented adverse effects. This study delineated their inter-regional variations in road dust collected from urban/suburb, agricultural, and forest areas, and screened for less-studied AAL/O analogues with high-resolution mass spectrometry. 1,3-Diphenylguanidine (DPG; median concentration: 121 ng/g) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q; 9.75 ng/g) are the most abundant congeners, constituting 69.7% and 41.4% of the total concentrations of AAL/Os (192 ng/g) and those of AAO transformation products (22.3 ng/g), respectively. The spatial distribution across the studied sites suggests evident human impacts, reflected by the pronounced urban signature and vehicle-originated pollution. Our nontargeted analysis of the most-contaminated road dust identified 16 AAL/O-related chemicals, many of which have received little investigation. Particularly, environmental and toxicological information remains extremely scarce for five out of the 10 most concerning compounds prioritized in terms of their dusty residues and toxicity including 1,2-diphenyl-3-cyclohexylguanidine (DPCG), N,N''-bis[2-(propan-2-yl)phenyl]guanidine (BPPG), and N-(4-anilinophenyl)formamide (PPD-CHO). Additionally, dicyclohexylamine (DChA), broadly applied as an antioxidant in automobile products, had an even greater median level than DPG. Therefore, future research on their health risks and (eco)toxic potential is of high importance.

Amino accelerators and antioxidants in sediments from the Dong Nai River System, Vietnam: Distribution and influential factors.

Amino accelerators and antioxidants (AAL/Os) have become a suite of contaminants of emerging concern recently due to the accumulating evidence for their environmental occurrence and associated toxic potential. Nevertheless, data on sedimentary deposition of AAL/Os has remained scarce, particularly for regions beyond the North America. In the present study, we elucidated spatial distribution of fifteen AAL/Os and five AAO transformation products (AAOTPs) in seventy-seven sediments from the Dong Nai River System (DNRS), Vietnam. Total concentrations of AAL/Os (∑AAL/Os) ranged from 0.377 to 51.4 ng/g (median: 5.01 ng/g). 1,3-Diphenylguanidine and 4,4'-bis(1,1-dimethylbenzyl) diphenylamine were the two most prevalent congeners, both with detection frequencies >80%. Additionally, AAOTPs were quantifiable in 79% of the DNRS sediments with a median ∑AAOTPs at 2.19 ng/g, dominated by N, N'-diphenylbenzidine and 2-nitrodiphenylamine. Higher sediment-associated levels of AAL/Os and AAOTPs were spotted in downstream and the primary tributary of the DNRS compared to the upstream, implying their cumulative sedimentation towards the estuarine region. The distribution patterns of AAL/Os and AAOTPs across individual transects also demonstrated the influence of human activities (e.g., urbanization and agriculture), hydrodynamics, and decontamination by mangrove reserves. Meanwhile, characteristics of sediments, i.e., total organic carbon (TOC) content and grain sizes, exhibited significant correlations with the burdens of these compounds, indicating their preferential partitioning into the fine and TOC-rich matter. This research sheds light on environmental behavior of AAL/Os and AAOTPs beneath Asian aquatic system, and highlights the need for further evaluation of their impacts on the wildlife and public health.

Emerging technologies for cancer therapy using accelerated particles.

Cancer therapy with accelerated charged particles is one of the most valuable biomedical applications of nuclear physics. The technology has vastly evolved in the past 50 years, the number of clinical centers is exponentially growing, and recent clinical results support the physics and radiobiology rationale that particles should be less toxic and more effective than conventional X-rays for many cancer patients. Charged particles are also the most mature technology for clinical translation of ultra-high dose rate (FLASH) radiotherapy. However, the fraction of patients treated with accelerated particles is still very small and the therapy is only applied to a few solid cancer indications. The growth of particle therapy strongly depends on technological innovations aiming to make the therapy cheaper, more conformal and faster. The most promising solutions to reach these goals are superconductive magnets to build compact accelerators; gantryless beam delivery; online image-guidance and adaptive therapy with the support of machine learning algorithms; and high-intensity accelerators coupled to online imaging. Large international collaborations are needed to hasten the clinical translation of the research results.

Physics successfully implements Lagrange multiplier optimization.

Optimization is a major part of human effort. While being mathematical, optimization is also built into physics. For example, physics has the Principle of Least Action; the Principle of Minimum Power Dissipation, also called Minimum Entropy Generation; and the Variational Principle. Physics also has Physical Annealing, which, of course, preceded computational Simulated Annealing. Physics has the Adiabatic Principle, which, in its quantum form, is called Quantum Annealing. Thus, physical machines can solve the mathematical problem of optimization, including constraints. Binary constraints can be built into the physical optimization. In that case, the machines are digital in the same sense that a flip-flop is digital. A wide variety of machines have had recent success at optimizing the Ising magnetic energy. We demonstrate in this paper that almost all those machines perform optimization according to the Principle of Minimum Power Dissipation as put forth by Onsager. Further, we show that this optimization is in fact equivalent to Lagrange multiplier optimization for constrained problems. We find that the physical gain coefficients that drive those systems actually play the role of the corresponding Lagrange multipliers.

Power-Intent Systolic Array Using Modified Parallel Multiplier for Machine Learning Acceleration.

Systolic arrays are an integral part of many modern machine learning (ML) accelerators due to their efficiency in performing matrix multiplication that is a key primitive in modern ML models. Current state-of-the-art in systolic array-based accelerators mainly target area and delay optimizations with power optimization being considered as a secondary target. Very few accelerator designs directly target power optimizations and that too using very complex algorithmic modifications that in turn result in a compromise in the area or delay performance. We present a novel Power-Intent Systolic Array (PI-SA) that is based on the fine-grained power gating of the multiplication and accumulation (MAC) block multiplier inside the processing element of the systolic array, which reduces the design power consumption quite significantly, but with an additional delay cost. To offset the delay cost, we introduce a modified decomposition multiplier to obtain smaller reduction tree and to further improve area and delay, we also replace the carry propagation adder with a carry save adder inside each sub-multiplier. Comparison of the proposed design with the baseline Gemmini naive systolic array design and its variant, i.e., a conventional systolic array design, exhibits a delay reduction of up to 6%, an area improvement of up to 32% and a power reduction of up to 57% for varying accumulator bit-widths.

Computational Study of a Motion Sensor to Simultaneously Measure Two Physical Quantities in All Three Directions for a UAV.

Cross-axis sensitivity is generally undesirable, and lower values are required for the accurate performance of a thermal accelerometer. In this study, errors in devices are utilized to simultaneously measure two physical quantities of an unmanned aerial vehicle (UAV) in the X-, Y-, and Z-directions, i.e., where three accelerations and three rotations can also be simultaneously measured using a single motion sensor. The 3D structures of thermal accelerometers were designed and simulated in a FEM simulator using commercially available FLUENT 18.2 software Obtained temperature responses were correlated with input physical quantities, and a graphical relationship was created between peak temperature values and input accelerations and rotations. Using this graphical representation, any values of acceleration from 1g to 4g and rotational speed from 200 to 1000°/s can be simultaneously measured in all three directions.

Deep Learning Accelerators' Configuration Space Exploration Effect on Performance and Resource Utilization: A Gemmini Case Study.

Though custom deep learning (DL) hardware accelerators are attractive for making inferences in edge computing devices, their design and implementation remain a challenge. Open-source frameworks exist for exploring DL hardware accelerators. Gemmini is an open-source systolic array generator for agile DL accelerator exploration. This paper details the hardware/software components generated using Gemmini. The general matrix-to-matrix multiplication (GEMM) of different dataflow options, including output/weight stationary (OS/WS), was explored in Gemmini to estimate the performance relative to a CPU implementation. The Gemmini hardware was implemented on an FPGA device to explore the effect of several accelerator parameters, including array size, memory capacity, and the CPU/hardware image-to-column (im2col) module, on metrics such as the area, frequency, and power. This work revealed that regarding the performance, the WS dataflow offered a speedup of 3× relative to the OS dataflow, and the hardware im2col operation offered a speedup of 1.1× relative to the operation on the CPU. For hardware resources, an increase in the array size by a factor of 2 led to an increase in both the area and power by a factor of 3.3, and the im2col module led to an increase in area and power by factors of 1.01 and 1.06, respectively.

Hardware-Software Partitioning for Real-Time Object Detection Using Dynamic Parameter Optimization.

Computer vision algorithms implementations, especially for real-time applications, are present in a variety of devices that we are currently using (from smartphones or automotive applications to monitoring/security applications) and pose specific challenges, memory bandwidth or energy consumption (e.g., for mobility) being the most notable ones. This paper aims at providing a solution to improve the overall quality of real-time object detection computer vision algorithms using a hybrid hardware-software implementation. To this end, we explore the methods for a proper allocation of algorithm components towards hardware (as IP Cores) and the interfacing between hardware and software. Addressing specific design constraints, the relationship between the above components allows embedded artificial intelligence to select the operating hardware blocks (IP cores)-in the configuration phase-and to dynamically change the parameters of the aggregated hardware resources-in the instantiation phase, similar to the concretization of a class into a software object. The conclusions show the benefits of using hybrid hardware-software implementations, as well as major gains from using IP Cores, managed by artificial intelligence, for an object detection use-case, implemented on a FPGA demonstrator built around a Xilinx Zynq-7000 SoC Mini-ITX sub-system.

The Role of Hydrogen Incorporation into Amorphous Carbon Films in the Change of the Secondary Electron Yield.

Over the last few years, there has been increasing interest in the use of amorphous carbon thin films with low secondary electron yield (SEY) to mitigate electron multipacting in particle accelerators and RF devices. Previous works found that the SEY increases with the amount of incorporated hydrogen and correlates with the Tauc gap. In this work, we analyse films produced by magnetron sputtering with different contents of hydrogen and deuterium incorporated via the target poisoning and sputtering of CxDy molecules. XPS was implemented to estimate the phase composition of the films. The maximal SEY was found to decrease linearly with the fraction of the graphitic phase in the films. These results are supported by Raman scattering and UPS measurements. The graphitic phase decreases almost linearly for hydrogen and deuterium concentrations between 12% and 46% (at.), but abruptly decreases when the concentration reaches 53%. This vanishing of the graphitic phase is accompanied by a strong increase of SEY and the Tauc gap. These results suggest that the SEY is not dictated directly by the concentration of H/D, but by the fraction of the graphitic phase in the film. The results are supported by an original model used to calculate the SEY of films consisting of a mixture of graphitic and polymeric phases.

Structural Characterization of Several Cement-Based Materials Containing Chemical Additives with Potential Application in Additive Manufacturing.

The rapid increase in additive manufacturing applications in all industries has highlighted the lack of innovative technologies and processes in the construction industry. Several European and international policies are in place to guide the development of the technological processes involved in the construction industry toward a sustainable future. Considering the global concerns regarding this industry, the purpose of this study was to develop new cement-based materials that are capable of accelerated hydration and early strength development for use in additive manufacturing. Ca(NO3)2·4H2O, Al2(SO4)3·18H2O and Na2S2O3·5H2O were used to obtain the accelerating effect in the hydration of Portland cement. Based on results obtained from X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX) techniques, as well as low-field nuclear magnetic resonance relaxometry (LF-NMR) techniques, it was demonstrated that all accelerators used have a quickening effect on cement hydration. The addition of Na2S2O3·5H2O or combined Na2S2O3·5H2O and Ca(NO3)2·4H2O led to obtaining new cement-based materials with early strength development and fast hydration of microorganized internal structures, critical characteristics for 3D printing.

Medical linac photon skyshine: Monte Carlo calculations and a methodology for estimates.

It has been shown that a widely quoted formula for estimating medical linac photon skyshine equivalent doses is erroneous. Monte Carlo calculations have been performed to develop an easy method for quickly and accurately estimating skyshine radiation levels and to gain improved physical insight into the skyshine phenomenon. Calculations of linac photon skyshine have been performed for 4, 6, 10, 15, and 18 MV beams for 10 × 10 cm2 and 40 × 40 cm2 fields and for a range of room dimensions and roof thicknesses. The effect of flattening filter free beams has been considered. Air kerma rates (AKRs) can be accurately fitted to a simple algebraic formula that is a function of the horizontal distance from the isocenter with a single energy dependent fitting parameter. The AKR, at a height of 1.3 m above level ground, reaches a local maximum at a distance dmax  = 1.5dw + 1.1h, where dw is the horizontal distance from the isocenter to the outside of the side wall, and h is the vertical distance from the isocenter to the top of the roof. For thin roofs, low energy beams lead to significantly more skyshine than high energy beams because low energy photons are more easily scattered through large angles. In the absence of a roof, the maximum skyshine dose rate is on the order of 8 × 10-7 times the dose rate at isocenter. The average energy of the skyshine photons is about 0.15 MeV, and it is remarkably independent of almost all parameters. A simple methodology is outlined for the evaluation of photon skyshine.