Local Radiation Effects Research Articles

OXIDATIVE AND ANTIOXIDANT PROCESSES IN THE FOCUS OF THE SKIN EXPOSED TO LOCAL ULTRAVIOLET IRRADIATION

The purpose of this study was to investigate the effect of local ultraviolet radiation on the content of lipid peroxidation products, lipofuscin, and the functioning of antioxidant enzymes in the skin of guinea pigs. Materials and methods. The studies were performed on 24 albino guinea pigs exposed to a single local ultraviolet radiation. The control group was made up of intact animals. The content of primary (diene conjugates) and secondary (TAC-active products) lipid peroxidation products, the activity of antioxidant enzymes (superoxide dismutase and catalase), and the content of lipofuscin were assessed in the skin in 2 hours, 4 hours, and on the 3rd and 8th day following the UV irradiation. Results. Under the influence of local ultraviolet radiation, all guinea pigs develop erythema (its peak is observed in 4 hours, and on the 3rd day), which disappears on the 8th day. There is a sharp enhancement of lipid peroxidation processes due to the accumulation of lipid peroxidation primary and secondary products in the skin of guinea pigs in all periods of the experiment. In parallel with the increase in lipid peroxidation products, there is a decrease in the activity of antioxidant enzymes (catalase and superoxide dismutase) in the focus of radiation. The content of lipofuscin in the skin progressively increases throughout the study period. Conclusions. The early erythema period following the local ultraviolet irradiation in the skin of guinea pigs, is characterized by increased content of diene conjugates and TBA-active products (in 2, 4 hours, on the 3rd day); decreased catalase activity and increased lipofuscin concentration (on the 3rd day after irradiation). The early post-erythema period (8th day) following the local ultraviolet irradiation is characterized by the accumulation of diene conjugates, TBA-active products and lipofuscin against the background of a decrease in the activity of catalase and superoxide dismutase in the skin of guinea pigs.

The Dominant Role of Snow/Ice Albedo Feedback Strengthened by Black Carbon in the Enhanced Warming over the Himalayas

AbstractAn obvious warming trend in winter over the Tibetan Plateau (TP) in the recent decades has been widely discussed, with studies emphasizing the dominant effects of local radiative factors, including those due to black carbon (BC). The Himalayas are one of the largest snowpack- and ice-covered regions in the TP, and an ideal area to investigate local radiative effects on climate change. In this study, the coupled climate feedback response analysis method (CFRAM) is applied to quantify the magnitude of warming over the Himalayas induced by different external forcing factors and climate feedback processes. The results show that snow/ice albedo feedback (SAF) resulted in a warming of approximately 2.6°C and was the primary contributor to enhanced warming over the Himalayas in recent decades. This warming was much greater than the warming induced by dynamic and other radiative factors. In particular, the strong radiative effects of BC on the warming over the Himalayas are identified by comparing control and BC-perturbed experiments of the Community Earth System Model (CESM). As a result of strong BC effects on the Himalayas, evaporation and reduced precipitation were strengthened, accounting for local drying and land degradation, which intensified warming. These results suggest that more investigations on the local radiative effects on the climate and ecosystem are needed, especially in the high-altitude cryosphere.

Short-term influences of radiation on musculofascial healing in a laparotomy rat model

Preoperative radiation is associated with an increased risk of wound complications. However, the influences of radiation on musculofascial wound healing remains unclear. The purpose of the study was to investigate the short-term effects of preoperative local radiation on the musculofascial healing of laparotomy incisions in a rat model. Eighteen Fischer 344 rats received radiation doses of 0, 10, or 20 Gy to the abdominal wall and underwent laparotomy 4 weeks later. Two weeks after laparotomy, samples of irradiated muscle were harvested for mechanical tests, histological (Hematoxylin & Eosin, and Masson’s Trichrome) and immunohistochemical analyses using KI67, CD31, TGF-β, and MYOD1 antibodies. The elastic modulus (EM), maximum strain (MS), and ultimate tensile strength (UTS) in the 20-Gy group were significantly weaker than those in the 0-Gy group. The EM and UTS in the 20-Gy group were significantly lower than those in the 10-Gy group. The UTS and MS in the 10-Gy group were significantly lower than those in the 0-Gy group. The mean number of inflammatory cells per mm2 in the 20-Gy group was significantly larger than those in the 10- and 0-Gy groups. The mean numbers of CD31-, KI67-, and MYOD1-positive cells, the optical density of TGF-β, and the microvessel density in the 20-Gy group were significantly smaller than those in the 10- and 0-Gy groups. These results indicated that radiation delays musculofascial healing and decreases mechanical strength of the laparotomy incision by creating a chronic inflammatory environment, inhibiting cell proliferation, angiogenesis, granulation maturation, collagen deposition, and muscular regeneration in a dose-dependent manner. The impaired biomechanical, histological and molecular properties may be associated with the higher risk of wound complications in patients who undergo radiotherapy prior to laparotomy.

Simulations of a turbulent line fire with a steady flamelet combustion model coupled with models for non-local and local gas radiation effects

The general objective of this study is to develop accurate combustion and radiation models for large eddy simulations (LES) of well-controlled laboratory-scale turbulent fires. The combustion model features a library of flamelet solutions corresponding to steady, laminar, strained diffusion flames. The radiation model features a classical description of non-local radiation phenomena through the Radiative Transfer Equation (RTE). Different treatments of coupled combustion and radiation effects at flamelet scale are considered: a treatment in which local radiation phenomena are neglected inside the flamelet solver; and a treatment in which these phenomena are included inside the flamelet solver and also subgrid-scale turbulence-radiation interactions are included in the RTE solver. This modeling framework is incorporated into the LES solver FireFOAM, developed by FM Global. It is evaluated in simulations of a buoyancy-driven, methane-air, turbulent diffusion flame experimentally characterized by measurements of local temperatures and global flame emissive power. Comparisons between simulated and measured temperatures show significant discrepancies that may be explained by overestimated values of the width of the presumed probability density function representing subgrid-scale variations of mixture fraction. Similar comparisons for the global radiative loss fraction show good agreement provided that local radiation phenomena and turbulence-radiation interactions are included in the model.

Long-Term Supratentorial Radiologic Effects of Surgery and Local Radiation in Children with Infratentorial Ependymoma

Current standard of care for children with infratentorial ependymoma includes maximal safe resection and local radiation of 54-59 Gray. High-dose local radiation has been associated with declines in multiple cognitive domains. The anatomic and physiologic correlates of this cognitive decline remain undefined, and there have been no radiographic studies on the long-term effects of this treatment paradigm. A comprehensive database of pediatric brain tumor patients treated at Stanford Children's from 2004-2016 was queried. Seven patients with posterior fossa ependymoma who were treated with surgery and local radiation alone, who had no evidence of recurrent disease, and had imaging suitable for analysis were identified. Diffusion-weighted magnetic resonance imaging datasets were used to calculate apparent diffusion coefficient maps for each subject, while arterial spin labeling datasets were used to calculate maps of cerebral blood flow. Diffusion-weighted imaging and arterial spin labeling datasets of 52 age-matched healthy children were analyzed in the same fashion to enable group comparisons. Several statistically significant differences were detected between the 2 groups. Cerebral blood flow was lower in the caudate and pallidum and higher in the nucleus accumbens in the ependymoma cohort compared with controls. Apparent diffusion coefficient was increased in the thalamus and trended toward decreased in the amygdala. Surgery and local radiation for posterior fossa ependymoma are associated with supratentorial apparent diffusion coefficient and cerebral blood flow alterations, which may represent an anatomic and physiologic correlate to the previously published decline in neurocognitive outcomes in this population.

Field measurements of solid-fuel cookstove emissions from uncontrolled cooking in China, Honduras, Uganda, and India

Cookstoves have wide-reaching impacts on human health, air quality, and the climate. We measured emissions from uncontrolled cooking in 41 households in China, Honduras, Uganda, and India using a portable sampler. Test sites were chosen to cover a range of stove types (traditional and “improved”), fuels (wood, charcoal and coal), and cooking practices. We report test-integrated fuel-based emission factors (EFs) of fine particulate matter (PM2.5) mass, organic carbon (OC), elemental carbon (EC), as well as real time EFs of carbon monoxide (CO), black carbon (BC), total particle number, and particle size distributions. There was substantial house-to-house variability in emissions; the distribution of EFs were also highly positively skewed by several “superemitter” stoves in China (those with PM2.5 EFs 5–20 times greater than the median value). The highest PM2.5 mass emission factors were measured in China (median:10.3 g/kg-fuel), and the lowest in Uganda (median: 1.7 g/kg-fuel). The median PM2.5 mass EFs in wood-burning stoves in Honduras and India were similar: 3.7 g/kg-fuel and 4.1 g/kg-fuel, respectively. However, Indian stoves had higher EC EFs then Honduran stoves, demonstrating that emissions depend on more that fuel type; regional differences, such as cooking styles and stove design, may influence aerosol properties as well. Coal and charcoal stoves had higher OC:EC than wood stoves. The differences between the CO, PM2.5, and OC:EC ratios of “improved” and traditional stoves in India and Honduras were not statistically significant. To the best of our knowledge, we report the first cookstove source size distributions measurements from uncontrolled in-home cooking. These distributions varied between countries, which will influence local radiative effects. Particle size distributions from stoves tested in China, Honduras, and India were unimodal in the size range measured, with geometric mean diameters (GMDs) of 66 nm, 48 nm, and 76 nm, respectively. The median GMD of particles emitted from Ugandan charcoal stoves was 39, and when all tests are averaged, the resulting distribution appears tri-modal, with modes near 15, 30, and 100 nm. Real-time emissions data reveal high BC and particle number emissions during startup and fuel additions, which can be seen in the positively skewed distributions. Emissions of BC were most skewed, indicating that they were highly event-driven, followed by total particle number. CO emissions were more evenly spread across cooking events.

Amelioration of Head and Neck Radiation-Induced Mucositis and Distant Marrow Suppression in Fanca-/- and Fancg-/- Mice by Intraoral Administration of GS-Nitroxide (JP4-039).

Squamous cell carcinomas of the head and neck are appearing with increased frequency in both marrow transplanted and non-transplanted Fanconi anemia (FA) patients. FA patients commonly display radiosensitivity of epithelial tissues, complicating effective radiotherapy. Fancd2-/- mice (C57BL/6J and 129/Sv background) demonstrate epithelial tissue sensitivity to single-fraction or fractionated irradiation to the head and neck and distant marrow suppression (abscopal effect), both ameliorated by intraoral administration of the mitochondrial-targeted antioxidant, GS-nitroxide, JP4-039. We now report that mice of two other FA genotypes, Fancg-/- (B6) and the most prevalent human genotype Fanca-/- (129/Sv), also demonstrate: 1. reduced longevity of hematopoiesis in long-term bone marrow cultures; 2. radiosensitivity of bone marrow stromal cell lines; and 3. head and neck radiation-induced severe mucositis and abscopal suppression of distant marrow hematopoiesis. Intraoral administration of JP4-039/F15, but not non-mitochondrial-targeted 4-amino-Tempo/F15 or F15 alone, prior to each radiation treatment ameliorated both local and abscopal radiation effects. Head and neck irradiated TGF-β-resistant SMAD3-/- (129/Sv) mice and double-knockout SMAD3-/- Fancd2-/- (129/Sv) mice treated daily with TGF-β receptor antagonist, LY364947, still displayed abscopal bone marrow suppression, implicating a non-TGF-β mechanism. Thus, amelioration of both local normal tissue radiosensitivity and distant marrow suppression by intraoral administration of JP4-039 in Fancg-/- and Fanca-/- mice supports a clinical trial of this locally administered normal tissue radioprotector and mitigator during head and neck irradiation in FA patients.

Texture analysis of T1-w and T2-w MR images allows a quantitative evaluation of radiation-induced changes of internal obturator muscles after radiotherapy for prostate cancer.

To investigate the potential of texture analysis applied on T2-w and postcontrast T1-w images acquired before radiotherapy for prostate cancer (PCa) and 12months after its completion in quantitatively characterizing local radiation effect on the muscular component of internal obturators, as organs potentially involved in urinary toxicity. T2-w and postcontrast T1-w MR images were acquired at 1.5T before treatment (MRI1) and at 12months of follow-up (MRI2) in 13 patients treated with radiotherapy for PCa. Right and left internal obturator muscle contours were manually delineated upon MRI1 and then automatically propagated on MRI2 by an elastic registration method. Planning CT images were coregistered to both MRIs and dose maps were deformed accordingly. A high-dose region receiving >55Gy and a low-dose region receiving <55Gy were identified in each muscle volume. Eighteen textural features were extracted from each region of interest and differences between MRI1 and MRI2 were evaluated. A signal increase was highlighted in both T2-w and T1-w images in the portion of the obturators near the prostate, i.e., in the region receiving medium-high doses. A change in the spatial organization was identified, as an increase in homogeneity and a decrease in contrast and complexity, compatible with an inflammatory status. In particular, the region receiving medium-high doses presented more significant or, at least, stronger differences. Texture analysis applied on T1-w and T2-w MR images has demonstrated its ability in quantitative evaluating radiation-induced changes in obturator muscles after PCa radiotherapy.

Implications of HER2 Status on Local Control and Adverse Radiation Effects After Stereotactic Radiosurgery for Brain Metastases of Breast Cancer

Implications of HER2 Status on Local Control and Adverse Radiation Effects After Stereotactic Radiosurgery for Brain Metastases of Breast Cancer

Refining Estimates of Local Failure and Adverse Radiation Effect for Brain Metastases Treated with Radiosurgery

Refining Estimates of Local Failure and Adverse Radiation Effect for Brain Metastases Treated with Radiosurgery

136 Long-term Supratentorial Radiographic Effects of Surgery and Local Radiation in Children with Infratenorial Ependymoma

Abstract INTRODUCTION Current standard of care for children with an infratentorial ependymoma includes maximal safe resection with local radiation of 54–59gy. High-dose local radiation has been associated with decline in multiple cognitive domains. The anatomic correlates of this cognitive decline remain undefined and there have been no radiographic studies on the long-term effects of this treatment paradigm. METHODS A comprehensive database of pediatric brain tumor patients treated at Stanford Children's from 2004–2016 was queried. 7 patients with posterior fossa ependymoma were identified who were treated with surgery and local radiation alone, who had no evidence of recurrent disease, and had imaging suitable for analysis. Diffusion-weighted MRI (DWI) datasets were used to calculate apparent diffusion coefficient (ADC) maps for each subject, while arterial spin labeling (ASL) datasets were used to calculated maps of cerebral blood flow (CBF). Using an atlas-based approach, the following brain structures were automatically segmented: cerebral white matter, cerebral cortex, thalamus, caudate, putamen, pallidum, hippocampus, amygdala, and accumbens. Furthermore, DWI and ASL datasets of 52 age-matched healthy children were available and analyzed in the same fashion to enable group comparisons. Binomial logistic regression models were developed for CBF and ADC measurements with disease status as a binary response variable and a significance threshold of P &lt; 0.05. RESULTS &gt;Several statistically significant differences were detected between the two groups. CBF was lower in the caudate (OR = .424 95%CI.142-.838 p = .05) and pallidum (OR = .479 95%CI = .204-.808 p = .029) and higher in the accumbens (OR = 1.917 95%CI = 1.182-4.472 p = .046) in the ependymoma cohort compared to controls. ADC was increased in the thalamus (OR = 1.168 95%CI = 1.040-1.407 p = .027) and trended towards decreased in the amygdala (OR = .93 95%CI = .846-.996 P = 0.068). CONCLUSION Surgery and local radiation for posterior fossa ependymoma are associated with supratentorial ADC and CBF alterations which may represent an anatomical and physiologic correlate to the previously published decline in neurocognitive outcomes in this population.

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day−1. To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations. Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes. The cloud fields in the 100 and 50 m resolution simulations develop similarly; however, 3-D local effects are stronger in the 100 m simulations which might indicate a limit of our 3-D radiation parameterization.

Laser equipment for hardness evaluation of semiconductor elements exposed to heavy charged particles (Review)

A review of laser devices that are currently used to perform hardness evaluation of microelectronic devices that are exposed to heavy charged particles, with respect to local radiation effects is presented. A brief classification of ionization effects in semiconductors caused by single heavy charged particles is provided. The possibility of using focused pulse-laser radiation for research on these effects is validated. A general approach to the construction of test systems that are based on picosecond lasers with sharp beam focusing systems is presented. The technical requirements for the basic modules of such systems are substantiated. The parameters of the domestic PICO-3 and PICO-4 laser test devices are compared to their foreign analogues and the means of their further improvement are given. The technical and operational characteristics of these devices that allow them to be used in various research tasks that require selective (with a submicron spatial resolution) object excitation by ultrashort laser pulses and recording of its response with exact timing of the moment of excitation, as well as for various precise technological operations, are discussed.

Dequalinium blocks macrophage-induced metastasis following local radiation

A major therapeutic obstacle in clinical oncology is intrinsic or acquired resistance to therapy, leading to subsequent relapse. We have previously shown that systemic administration of different cytotoxic drugs can induce a host response that contributes to tumor angiogenesis, regrowth and metastasis. Here we characterize the host response to a single dose of local radiation, and its contribution to tumor progression and metastasis. We show that plasma from locally irradiated mice increases the migratory and invasive properties of colon carcinoma cells. Furthermore, locally irradiated mice intravenously injected with CT26 colon carcinoma cells succumb to pulmonary metastasis earlier than their respective controls. Consequently, orthotopically implanted SW480 human colon carcinoma cells in mice that underwent radiation, exhibited increased metastasis to the lungs and liver compared to their control tumors. The irradiated tumors exhibited an increase in the colonization of macrophages compared to their respective controls; and macrophage depletion in irradiated tumor-bearing mice reduces the number of metastatic lesions. Finally, the anti-tumor agent, dequalinium-14, in addition to its anti-tumor effect, reduces macrophage motility, inhibits macrophage infiltration of irradiated tumors and reduces the extent of metastasis in locally irradiated mice. Overall, this study demonstrates the adverse effects of local radiation on the host that result in macrophage-induced metastasis.

Effects of Local Radiation Combined with Chemotherapy in the treatment of Patients with Extensive-stage Small Cell Lung Cancer

背景与目的化疗作为广泛期小细胞肺癌（extensive-stage small cell lung cancer, ES-SCLC）的主要治疗方法，其有效率高，但容易发生快速耐药。局部治疗作为姑息治疗方法，能够缓解局部症状和提高患者生活质量，但是能否延长生存期尚缺乏证据。本研究旨在分析在全身化疗基础上的局部放疗对ES-SCLC患者生存的作用与影响。方法回顾性分析302例ES-SCLC患者临床资料，采用Kaplan-Meier法及Cox多因素回归分析预后因素。结果全组患者中位无进展生存期（progression-free survival, PFS）4.4个月，中位生存期（median survival time, MST）10.4个月，1年生存率37.8%；2年生存率10.2%；3年生存率4.4%。原发灶放疗+化疗组和单纯化疗组患者MST分别为14.3个月和8.2个月（P < 0.01）；多处转移灶局部治疗、一处转移灶局部治疗和未行转移灶局部治疗患者MST分别为18.7个月、12.3个月和8.9个月（P < 0.01）；主动性的转移灶局部治疗、被动性的转移灶局部治疗和未行转移灶局部治疗患者MST分别为16.0个月、10.9个月和9.4个月（P < 0.01）；全脑预防性照射治疗（prophylactic cranial irradiation, PCI）和未行PCI患者MST分别为19.8个月和9.9个月（P < 0.01）。原发灶放疗、转移灶局部治疗和PCI是ES-SCLC患者的独立预后因素（P < 0.01）。结论原发灶放疗、转移灶局部治疗和PCI能够延长ES-SCLC患者生存期。

Decorporation agents for internal radioactive contamination

When radionuclides are accidentally ingested or inhaled, blood circulation or tissue/organ deposition of the radionuclides causes systemic or local radiation effects. In such cases, decorporation therapy is used to reduce the health risks due to their intake. Decorporation therapy includes reduction and/or inhibition of absorption from the gastrointestinal tract, isotopic dilution, and the use of diuretics, adsorbents, and chelating agents. For example, penicillamine is recommended as a chelating agent for copper contamination, and diethylene triamine pentaacetic acid is approved for the treatment of internal contamination with plutonium. During chelation therapy, the removal effect of the drugs should be monitored using a whole-body counter and/or bioassay. Some authorities, such as the National Council on Radiation Protection and Measurements and International Atomic Energy Agency, have reported recommended decorporation agents for each radionuclide. However, few drugs are approved by the US Food and Drug Administration, and many are off-label-use agents. Because many decontamination agents are drugs that have been available for a long time and have limited efficacy, the development of new, higher-efficacy drugs has been carried out mainly in the USA and France. In this article, in addition to an outline of decorporation agents for internal radioactive contamination, an outline of our research on decorporation agents for actinide (uranium and plutonium) contamination and for radio-cesium contamination is also presented.

Multi-wavelength Raman LIDAR for Use in Determining the Microphysical, Optical, and Radiative Properties of Mixed Aerosols

The Multi-wavelength Raman LIDAR (MRL) system was developed to enable a better understanding of the complex properties of aerosols in the atmosphere. In this study, the microphysical, optical, and radiative properties of mixed aerosols were retrieved using the discrete aerosol observation products from the MRL. The dust mixing ratio, which is the proportion of dust particles to the total mixed, was derived using the particle depolarization ratio. It was employed in the retrieval of backscattering and extinction coefficient profiles for dust and non-dust particles. The vertical profiles of aerosol optical properties were then used as input parameters in the inversion algorithm for the retrieval of microphysical parameters including the effective radius, refractive index, and the single scattering albedo (SSA). Those products were successfully applied to an analysis of radiative flux using a radiative transfer model. The relationship between the MRL derived extinction and aerosol radiative forcing (ARF) in short-wavelength was assessed over Gwangju, Korea. The results clearly demonstrate that the MRL-derived extinction profiles are a good surrogate for use in the estimation of optical, microphysical, and radiative properties of aerosols. It is considered that the analytical results shown in this study can be used to provide a better understanding of air quality and the variation of local radiative effects due to aerosols.

The Impact of the Polarization Orientation on Laser SEE Modeling in Complex ICs

Numerical and experimental evaluation of the influence of laser radiation polarization orientation on ionization response of 180-nm and 90-nm CMOS ICs is performed. Comparative research is carried out to determine how the polarization of various sized laser beams affects the parameters of IC ionization response. The necessity of considering the orientation of laser radiation polarization for laser local radiation effect simulation is shown.

Process-model simulations of cloud albedo enhancement by aerosols in the Arctic.

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN), either through geoengineering or other increased sources of Arctic aerosols. An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Albedo increases are stronger for pure liquid clouds than mixed-phase clouds. Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus, the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation owing to precipitation changes are small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering is unlikely to be effective as the sole means of altering the global radiation budget but could have substantial local radiative effects.

Introduction to photobiology.

Photobiology is the study of the local and systemic effects of incident radiation on living organisms. Solar radiation is made up of ultraviolet, visible and infrared radiation. Ultraviolet radiation is made up of UV-C, UV-B, and UV-A. Sun exposure can lead to sunburn, tanning, vitamin D production, photoaging, and carcinogenesis. Phototherapy is the use of nonionizing radiation to treat cutaneous disease. Various types of artificial light sources are used for photo testing and phototherapy.