Fraction Of Absorbers Research Articles

Influence of the Oil Structuring System on Lipid Hydrolysis and Bioaccessibility of Healthy Fatty Acids and Curcumin.

Oleogels (OG) and gelled emulsions (GE) were elaborated with a mixture of olive and chia oils (80:20 ratio) without and with the incorporation of the health-related compound curcumin. These were studied to evaluate the influence of the oil structuring system on the lipid hydrolysis and bioaccessibility of three healthy fatty acids (FA) (palmitic, oleic, and α-linolenic acids) and of curcumin, compared to the oil mixture (bulk oil, BO). The oil structuring system influenced the firmness and texture, and the presence of curcumin significantly altered the color parameters. GE showed higher lipid digestibility, with a greater proportion of absorbable fraction (higher content of free FA and monoacylglycerides) than OG, which behaved similarly to BO. The presence of curcumin affected the degree of lipolysis, reducing lipid digestibility in OG and increasing it in GE. As for FA bioaccessibility, although GE presented higher percentages overall, curcumin significantly increased and decreased FA bioaccessibility in OG and GE, respectively. The oil structuring system also influenced the bioaccessibility of curcumin, which was higher in GE. Therefore, when selecting an oil structuring system, their physicochemical properties, the degree of lipid hydrolysis, and the bioaccessibility of both curcumin and the FA studied should all be considered.

Development and validation of a Medaka fish voxel-based model for internal ionizing radiation dosimetry

In this paper, we present a voxel-based phantom of Medaka fish that can be used to assess the internal radiation doses that would be absorbed by different organs of this fish species if exposed to radioactive wastewater released into the ocean. The geometric model for fish was generated based on available Wavefront Object files for smooth-bodied Medaka fish organs, whereas due to the lack of Medaka fish material specification, the material model was constructed using material data appropriate to ICRP 110 adult male voxel-based phantom. Absorbed Fractions (AFs) and Specific Absorbed Fractions (SAFs) were calculated for eight organs of major interest as sources and for each organ as target at a set of discrete photon, electron, alpha and neutron energies. To validate the present model the calculated AFs in the studied organs were compared to ones obtained in similar organs in a voxel-based phantom of another teleost fish species called Limanda limanda. The results presented are consistent with the reference dosimetric data. We concluded that the Medaka model can be used in radioecology research to improve marine radiation protection.

Phenolic bioaccessibility, antioxidant, and antidiabetic effects of indigenous fermented coffee beans after simulated gastrointestinal digestion and colonic fermentation

Postharvest fermentation could bring significant changes in the chemical profile of coffee beans so that the nutritional aspects. This study comprehensively evaluated the effects of indigenous fermentation on coffee beans in green and roasted status by quantifying the phenolic compounds and estimating their bioaccessibility, crude absorbability, antioxidant, enzyme inhibitory activity, and SCFA production during in vitro digestion and colonic fermentation. Compared to the unfermented (UF) beans, in both phenolic extract and absorbable fraction during digestion, fermented (F) coffee beans in roasted status showed similar or lower phenolic content and antioxidant activities. Only light-roasted FK showed significantly higher TPC (50.9 mg GAE/g) and TFC (1.21 mg QE/g) than the UFK (35.8 mg GAE/g, 1.06 mg QE/g) in the gastric absorbable fraction. However, medium-roasted FK performed significantly outstanding α-amylase (9.67%) and α-glucosidase (21.86%) inhibition activities than that of UFK (7.41%, 18.31%). The bioaccessibility and crude absorption rate of total phenolics and chlorogenic acid were relatively higher during the in vitro digestion and colonic fermentation of fermented green coffee beans. The differences were eventually eliminated along with the intensification of roasting due to the thermal degradation. The total SCFAs produced from fermented beans was only up to 2.185 mM after 16 h fecal reaction, which is significantly lower than that of the unfermented (<3.216 mM) because of the hydrolyzation of polysaccharides during the postharvest fermentation. Therefore, in the long term, fermented coffee beans could perform higher nutritional values with higher phenolic absorption efficiency, especially chlorogenic acids, and antidiabetic potential.

Construction of voxel-based Portunus haanii phantom and its absorbed fractions and specific absorbed fractions calculation based on Monte Carlo simulations

ObjectiveTo build the database of the absorbed fractions (AFs) and specific absorbed fractions (SAFs), in order to accurately assess the internal radiation dose in non-human biota. MethodsA voxel-based Portunus haanii phantom was established based on the computed tomography (CT) images. A set of AFs and SAFs were calculated with Monte Carlo toolkit Geant4 for the emission of monoenergetic photons and electrons with energies ranging from 10 ​keV to 5 ​MeV. ResultsThe mass of the voxel-based Portunus haanii phantom (392.2 ​g) was in agreement with the actual mass (389.2 ​g), indicating the reliability of the phantom. The calculated AFs and SAFs, based on the voxel-based Portunus haanii phantom, provided precise and reliable data for conducting internal radiation dose calculations specifically tailored to the Chinese Red Swimming Crab (Portunus haanii). The results indicated that the self-AFs and self-SAFs were affected by both the radiation energy and the mass of the source/target organ. Moreover, the AFs and SAFs for cross irradiation, were not only dependent on the energy and the mass of the target organ, but also on the relative position of the source and target organs. ConclusionThese results serve as a valuable resource for accurately evaluating the internal radiation exposure of this species.

Role of ionizing background on the statistics of metal absorbers in hydrodynamical simulations

ABSTRACT We study the statistical properties of O vi, C iv, and Ne viii absorbers at low-z (i.e. z &amp;lt; 0.5) using Sherwood simulations with ‘WIND’ only and ‘WIND + AGN’ feedback and massive black-II simulation that incorporates both ‘WIND’ i.e. outflows driven by stellar feedback and active galactic nucleus (AGN) feedbacks. For each simulation, by considering a wide range of metagalactic ionizing ultraviolet background (UVB), we show the statistical properties such as distribution functions of column density (N), b-parameter and velocity spread (ΔV90), the relationship between N and b-parameter, and the fraction of Ly α absorbers showing detectable metal lines as a function of N(H i) are influenced by the UVB used. This is because UVB changes the range in density, temperature, and metallicity of gas contributing to a given absorption line. For simulations considered here, we show the difference in some of the predicted distributions between different simulations is similar to the one obtained by varying the UVB for a given simulation. Most of the observed properties of O vi absorbers are roughly matched by Sherwood simulation with ‘WIND + AGN’ feedback when using the UVB with a lower O vi ionization rate. However, this simulation fails to produce observed distributions of C iv and fraction of H i absorbers with detectable metals. Therefore, in order to constrain different feedback processes and/or UVBs, using observed properties of H i and metal ions, it is important to perform simultaneous analysis of various observable parameters.

Stabilized soy protein emulsion enriched with silicon and containing or not methylcellulose as novel technological alternatives to reduce animal fat digestion

During the last decade, the consumption of animal saturated fat has been associated with an increased risk of chronic disease. Experience shows that changing the dietary habits of the population is a complicated and slow process, so technological strategies offer new possibilities for the development of functional foods. The present work is focused on studying the impact of using a food-grade non-ionic hydrocolloid (methylcellulose; MC) and/or the inclusion of silicon (Si) as a bioactive compound in pork lard emulsions stabilized with soy protein concentrate (SPC), on the structure, rheology, lipid digestibility and Si bioaccesibility during in vitro gastrointestinal digestion (GID). Four emulsions (SPC, SPC/Si, SPC/MC and SPC/MC/Si) were prepared with a final biopolymer (SPC and/or MC) concentration of 4% and 0.24% Si. The results showed a lower degree of lipid digestion in SPC/MC compared with SPC, specifically at the end of the intestinal phase. Moreover, Si partially reduced fat digestion only when incorporated into the SPC-stabilized emulsion, while this effect was lost in SPC/MC/Si. This was probably due to its retention inside the matrix emulsion, which resulted in lower bioaccesibility than in SPC/Si. Additionally, the correlation between the flow behavior index (n) and the lipid absorbable fraction was significant, suggesting that n can be a predictive marker of the extent of lipolysis. Concretely, our results revealed that SPC/Si and SPC/MC can be used as pork fat digestion reducers and thus, they can replace pork lard in the reformulation of animal products with potential health benefits.

Varietal Effect on Composition and Digestibility of Seedless Table Grapes (Vitis vinifera L.) under In Vitro Conditions.

Grapes are one of the richest sources of polyphenols in the Mediterranean diet and, therefore, a very good source of antioxidants in the human diet. For practical reasons, in recent years the market for seedless grape varieties has grown exponentially. These varieties are not well characterized yet, and therefore it is necessary to study the changes in composition that these new varieties bring in. Likewise, the effect of digestion on the bioavailability of polyphenols in foods of plant origin is well known, which, consequently, will also affect antioxidant activity and, in general, bioactivity. In this work, we studied the effect of the grape variety on the initial grape composition and on the absorbable fraction, as it would reach the intestine after in vitro digestion. Our results showed that black and red varieties have great potential for increasing the antioxidant content of the diet. Additionally, we have concluded that all polyphenols, with the exception of flavanols, see their bioavailable fraction diminished under in vitro conditions.

Simple interpretation of the seemingly complicated X-ray spectral variation of NGC 5548

ABSTRACT NGC 5548 is a very well-studied Seyfert 1 galaxy in broad wavelengths. Previous multiwavelength observation campaigns have indicated that its multiple absorbers are highly variable and complex. A previous study applied a two-zone partial covering model with different covering fractions to explain the complex X-ray spectral variation and reported a correlation between one of the covering fractions and the photon index of the power-law continuum. However, it is not straightforward to physically understand such a correlation. In this paper, we propose a model to avoid this unphysical situation; the central X-ray emission region is partially covered by clumpy absorbers composed of double layers. These ‘double partial coverings’ have precisely the same covering fraction. Based on our model, we have conducted an extensive spectral study using the data taken by XMM–Newton, Suzaku, and NuSTAR in the range of 0.3–78 keV for 16 yr. Consequently, we have found that the X-ray spectral variations are mainly explained by independent changes of the following three components; (1) the soft excess spectral component below ∼1 keV, (2) the cut-off power-law normalization, and (3) the partial covering fraction of the clumpy absorbers. In particular, spectral variations above ∼1 keV are mostly explained only by the changes of the partial covering fraction and the power-law normalization. In contrast, the photon index and all the other spectral parameters are not significantly variable.

Разработка и тестирование модели поглощения энергии в биообъектах от инкорпорированных излучателей фотонов

A new analytical method, previously developed for estimating beta absorbed fractions, was ex-tended for analytical estimating photon absorbed fractions in soft-tissue bodies from internal uni-formly distributed gamma emitters. The method involves a rescaling procedure with transfor-mation of real biological sizes to unitless effective ones combining information of both photon energy and object’s size. The rescaling was applied to large published datasets of photon ab-sorbed fractions in soft-tissue spheres. A new effect was demonstrated: the rescaled data were united into a single smooth “universal curve” with saturation. The universal curve for photon ab-sorbed fractions was described analytically as a function of a single argument – a rescaled effec-tive radius. Practical applicability of the approach for non-spherical convex bodies (ellipsoids) was demonstrated. Examples of analytical estimating the internal dose coefficients for repre-sentative terrestrial animals were calculated. The new method now available for electron and photon internal dosimetry, provides an effective analytical tool for calculating radiation absorbed fractions in organs and bodies of soft-tissue organisms.

Impact of Cooking Preparation on In Vitro Digestion of Eggs Simulating Some Gastrointestinal Alterations in Elders.

This study aimed to in vitro assess the impact of the cooking process of eggs (hard-boiled, poached, and omelet) on nutrients digestibility and vitamins A and D3 bioaccessibility under elderly gastrointestinal (GI) conditions. Three elderly digestion models were mimicked: oral (E1); oral and gastric (E2); and oral, gastric, and intestinal (E3), and a healthy adult model (C). Proteolysis extent reduced after digestion of omelet under the E3 model (p < 0.05) (up to 37% of reduction). Thus, hard-boiled and poached were more recommendable to enhance protein digestibility in elders. Altered GI conditions negatively influence neither the absorbable lipid fraction nor the cholesterol stability. Finally, vitamin A bioaccessibility was not affected but D3 slightly decreased with the elderly (E3). Hence, the digestion of nutrients was dependent on the resulting matrix, poached being the greater supplier of protein and lipid end-digestion products. Poached and omelet, however, offer a high net supply of bioaccessible vitamin D3 for elders.

In vitro dipeptidyl peptidase IV inhibitory activity and in situ insulinotropic activity of milk and egg white protein digests.

Dietary proteins are involved in the regulation of glucose homeostasis by different mechanisms. Food protein digestion products are reported to inhibit dipeptidyl peptidase IV (DPP-IV), induce incretin secretion or directly exert an insulinotropic effect in pancreatic β-cells. This study illustrates the DPP-IV inhibitory activity of gastric and intestinal digests of casein, whey and egg white proteins determined in vitro, using Gly-Pro-AMC, and in situ using non-differentiated Caco-2 cells. Comparable trends in the DPP-IV inhibitory profiles were obtained by these two methods although the extent of inhibition in situ was consistently lower than the inhibition observed in vitro. Casein intestinal digests and whey protein gastric and intestinal digests showed potent DPP-IV inhibitory activities in Caco-2 cells with IC50 values ranging from 0.8 to 1.2 mg mL-1. The absorbed fraction of the intestinal digests from whey and egg white protein induced insulin secretion in BRIN-BD11 cells when determined using a two-tiered cellular model (Caco-2 and BRIN-BD11). However, the gastric digests from the same substrates showed no insulin secretion. This may be related to limited trans-epithelial transport through the Caco-2 monolayer of the gastric digestion products. However, both, gastric and intestinal digests were able to induce insulin secretion in BRIN-BD11 cells when the monolayer was composed of a co-culture of STC-1 and Caco-2 cells. This result may be attributed to the activation of STC-1 cells and subsequent incretin secretion, induced by the gastric digest, as shown by an enhanced intracellular calcium uptake.

Modeling the statistics of the cold neutral medium in absorption-selected high-redshift galaxies

We present a statistical model of the selection function of cold neutral gas in high-redshift (z = 2.5) absorption systems. The model is based on the canonical two-phase model of the neutral gas in the interstellar medium and contains only one parameter for which we do not have direct observational priors: namely the central pressure of an L* halo at z = 2.5, P*. Using observations of the fraction of cold gas absorption in strong H I-selected absorbers, we were able to constrain P*. The model simultaneously reproduces the column density distributions of H I and H2, and we derived an expected total incidence of cold gas at z ∼ 2.5 of lCNM = 12 × 10−3. Compared to recent measurements of the incidence of C I-selected absorbers (EWλ 1560 &gt; 0.4 Å), the value of lCNM from our model indicates that only 15% of the total cold gas would lead to strong C I absorption (EW &gt; 0.4 Å). Nevertheless, C I lines are extremely useful probes of the cold gas as they are relatively easy to detect and provide direct constraints on the physical conditions. Lastly, our model self-consistently reproduces the fraction of cold gas absorbers as a function of NH I.

The Coevolution of Galaxies and the Cool Circumgalactic Medium Probed with the SDSS and DESI Legacy Imaging Surveys

Abstract We study the evolution of galaxies and the circumgalactic medium (CGM) through cosmic time by correlating ∼50,000 Mg ii absorbers, tracers of cool gas (∼104 K), detected in the Sloan Digital Sky Survey quasar spectra with galaxies detected in the DESI Legacy Imaging Surveys. By doing so, we extract the properties of galaxies associated with absorbers from redshift 0.4 to 1.3 with effectively ∼15,000 pairs and explore the covering fraction of Mg ii absorbers as a function of galaxy type, stellar mass, impact parameter, and redshift. We find that the gas covering fraction increases with stellar mass of galaxies by . However, after we normalize the impact parameter by the virial radius of dark matter halos, the gas profiles around galaxies with masses ranging from 109 to become weakly dependent on stellar mass. In addition, the gas distribution depends on galaxy type: the covering fraction within around star-forming galaxies is 2–4 times higher than that around passive galaxies at all redshifts. We find that the covering fraction of strong absorbers ( ) around both types of galaxies evolves significantly with redshift, similarly to the evolution of star formation rate (SFR) of galaxies, while such an evolution is not detected for weak absorbers ( ). We quantify the H i mass traced by strong absorbers and find that the gas mass around galaxies evolves consistently with the SFR of galaxies. This result suggests that the properties of galaxies and their CGM coevolve through cosmic time. Finally, we discuss the origins of strong absorbers around passive galaxies and argue that its redshift evolution may trace the star formation activity of satellite galaxies.

Cytotoxic Effect of Prodigiosin, Natural Red Pigment, Isolated from Serratia marcescens UFPEDA 398.

Prodigiosin is a secondary metabolite, with red pigmentation, produced by Serratia marcescens. Red pigment is a natural alkaloid whose chemical structure has three pyrrole rings. Prodigiosin has been described for several biological activities, including antitumor, inducing apotosis in T and B lymphocytes. This work aimed to evaluate the cytotoxic activity of prodigiosin in NCHI-292, HEp-2, MCF-7 and HL-60 tumor cell lines. The red pigment was isolated from Serratia marcescens UFPEDA 398 biomass whose fractions were previously separated by column chromatography, purified, identified and further characterized by GC-MS and compared with the computerized library of m/z values. The pigment corresponded to prodigiosin with maximum absorption at 534nm, molecular weight 323 and structural formula C20H25N3O. During the prodigiosin purification process a purple absorbance fraction at 272.65nm was also observed. Significant cytotoxic effects of prodigiosin were evidenced for NCHI-292, Hep-2, MCF-7 and HL-60 tumor cell lines. The isolated purple fraction had no cytotoxic effect (IC50 11.3µg/mL) when compared to prodigiosin (IC50 3.4µg/mL) for the tumor cell lines studied. The MCF-7 strain was slightly more pigment resistant (IC50 5.1µg/mL). Therefore, further studies will be needed to elucidate the antitumor mechanisms of prodigiosin action against tumor strains from flow cytometry tests. However, although these data are preliminary, it was evidenced that prodigiosin showed cytotoxic activity in tumor cell lines suggesting promising antitumor properties. In this sense, future studies on the cytotoxic and genotoxic effects of prodigiosin produced by S. marcecsens UFPEDA 398 are suggested.

Structurally designed hierarchical carbon nanotubes vertically anchored on elliptical-like carbon nanosheets with enhanced conduction loss as high-performance electromagnetic wave absorbent

Designing an effective conducting network to arouse conduction loss is an effective strategy to boost the microwave absorption properties while decreasing the filler weight fraction of absorbers in the matrix. Here, hierarchical carbon nanotubes vertically anchored on elliptical-like carbon nanosheets (Co/C nanosheet@CNTs composite) have been successfully prepared sintering of ZIF-67 in Ar/H2 flow, where the density and length of CNTs on Co/C nanosheet surfaces were effectively controlled by adjusting the heating temperature. When the pyrolysis temperature was 700 °C, high density of curved CNTs were formed on the surface of Co/C nanosheet surfaces and constructed an interconnected network, which resulted in the enhanced conduction loss as irradiated by microwave. Accordingly, it exhibited high-performance microwave absorbing, and the maximum reflection loss reached -51.8 dB GHz and the effective absorbing bandwidth (EAB) achieved 5.9 GHz with only 5 wt% additive in paraffin, which is even superior to the corresponding Co/C nanosheet composite with 10 wt% filler content. This work provides a new direction to fabricate carbon-based absorber with high-performance at low filler loading.

Development of a nonhuman primate computational phantom for radiation dosimetry.

The nonhuman primate (NHP) is an important animal model for evaluating the response of the human body to radiation exposure owing to similarities between its organ structure, genome, life span, and metabolism. However, there is a lack of radiation dosimetry estimations for NHPs. The aim of this work is to construct a computational phantom of NHPs and estimate absorbed fractions and specific absorbed fractions for internal radiation dosimetry. A female rhesus monkey was frozen and sectioned using a cryomacrotome. The transaxial sectioned images were imported into Adobe Photoshop for segmentation of internal organs. A total of 31 organs/tissues were identified and labeled. The segmented voxel phantom was then converted to a boundary representation (BREP) phantom to enable easy alteration of the phantom to mimic monkeys of different stature. The BREP model was then voxelized and imported into the MCNPX Monte Carlo radiation transport code for electron and photon dosimetry calculations. To estimate the appropriateness of using human phantoms as surrogate models for NHPs, absorbed fractions (AFs) and specific absorbed fractions (SAFs) of monoenergetic electrons and photons were calculated and compared with the ICRP reference newborn female phantom and a 1-yr-old female phantom. Considerable differences were observed for both self-absorbed and cross-absorbed doses for some organs between the NHP phantom and newborn phantom. For example, the ratios of the self-absorbed SAF(stomach wall) Monkey to SAF(stomach wall) Newborn ranged from 0.06 at 10keV to 0.29 at 3MeV for photons while the corresponding ratios to cross-absorbed SAF(liver→kidney) Monkey to SAF(liver→kidney) Newborn ranged from 0.78 at 50keV to 5.78 at 10keV for photons. Conversely, values of self-absorbed SAF were much higher (ratios of 2.39-4.19) for the brain and much lower for the uterus (0.51-0.61) in the monkey model compared to the newborn phantom. These dose differences can be attributed to the disparities between organ masses, shapes, and positions between the two phantoms. The developed NHP model can be exploited for the assessment of radiation dose to NHPs in preclinical radiation dosimetry studies and radiation therapy research.

Speciation analysis and dynamic absorption characteristics of heavy metals and deleterious element during growing period of Chinese peony

The heavy metals and deleterious element (Pd, Cd, Cu, As, and Hg) in Chinese peony (Paeonia lactiflora Pall.) were determined by Tessier’s sequence extraction method. Pb mainly existed in carbonate fraction. The main fraction of Cd in different tissues and different month is quite different. Cu mainly exists as exchangeable carbonate fractions. Five forms of Hg all exist in leaf, stem, and root. The total absorbable fraction of Pd, Cd, Cu, As, and Hg was different in different tissues. The total content of heavy metals can migrate from different tissues and the content of different speciation of heavy metal also can change during the growing period of plants. The results showed that different parts of plants and different elements resulted in different distribution and mobility. Base on this, it is more scientific and reasonable to clarify the migration and enrichment and to analyses the speciation of heavy metals during growing period of plant medicine. It is more scientific and reasonable to clarify the migration and enrichment, and to analyses the speciation of heavy metals during growing period of plant medicine.

A mechanistic model of photochemical transformation and degradation of colored dissolved organic matter

Photochemical degradation (PD) of colored dissolved organic matter (CDOM) is a key transformational process for both natural and anthropogenic DOM. A fully mechanistic model is presented that can simulate laboratory incubations of the controlled PD of marsh and estuarine derived CDOM. The model was designed and optimized to recreate the loss of absorbance for marsh low tide and estuarine samples, representing high molecular weight allochthonous and mid molecular weight estuarine CDOM. In the model, high specific absorbance fractions representative of marsh and estuarine CDOM are transformed into a low specific absorbance fraction representative of coastal ocean CDOM as well as non-colored fractions. The various transformations in the model have maximum apparent quantum yields (at 284 nm) that range from 3.22 × 10−8 ± 1.75 to 56.05 ± 21.5 [mmol C (mol photons)−1], with non-colored DOM/inorganic carbon production outpaced by inter-molecular organic carbon transformations. Model performance was tested using an independent incubation data set whereby experimental results of photobleaching of spectral absorbance at 300 nm were recreated with a Willmott model skill of 0.98 and mean percent error of −3.66%. The production of the low molecular weight photodegraded end member ranged from 0.52 to 4.86 μmol C L−1 h−1.

Gaia-assisted selection of a quasar reddened by dust in an extremely strong damped Lyman-α absorber at z = 2.226

Damped Lyman-α absorbers (DLAs) as a class of quasi-stellar object (QSO) absorption-line systems are currently our most important source of detailed information on the cosmic chemical evolution of galaxies. However, the degree to which this information is biased by dust remains to be understood. One strategy is to specifically search for QSOs that are reddened by metal-rich and dusty foreground absorbers. In this Letter, we present the discovery of a z = 2.60 QSO that is strongly reddened by dust in an intervening extremely strong DLA at z = 2.226. This QSO was identified through a novel selection that combined the astrometric measurements from ESA’s Gaia satellite with extisting optical and near- to mid-infrared photometry. We infer a total neutral atomic-hydrogen column density of log N(H I) = 21.95 ± 0.15 and a lower limit on the gas-phase metallicity of [Zn/H] &gt; −0.96. This DLA is also remarkable in that it exhibits shielded neutral gas that is visible in C I, and it shows tentative detections of CO molecular bands. The spectral energy distribution of the QSO is well accounted for by a spectral energy distribution that is normal for a QSO and is reddened by dust from a DLA with 10% solar metallicity, a dust extinction of AV = 0.82 ± 0.02 mag, and an extinction curve that resembles that of the Large Magellanic Cloud, including the characteristic 2175 Å extinction feature. Such QSO absorption-line systems have been shown to be very rare in previous surveys, which have mostly revealed sight-lines with low extinction. The present case therefore suggests that previous samples have under-represented the fraction of dusty absorbers. Building a complete sample of such systems is required to assess the significance of this effect.

Evaluation of Doses Absorbed to a Bone Marrow Stem Cell Layer from Short-lived Radionuclides in the Blood Vessels and from Long-lived Radionuclides in the Cortical Bone

The International Commission on Radiological Protection (ICRP) internal dose assessment model, currently adopted in Japanese regulation, assumes uniform distribution of radionuclides in bone marrow blood (ICRP Publication 60). Recent studies have revealed a localization of hematopoietic stem cells (HSCs) and immune cells in the perivascular region of the bone marrow sinusoids, suggesting a need to consider nonuniform distributions of the blood source and HSCs. To evaluate energy transfer to HSCs, a simplified model of cervical vertebrae with bone tissues and blood vessels was built using data from the adult Japanese male phantom. Doses absorbed by HSCs from blood and hard bone sources were calculated using a Monte Carlo simulation, and absorbed fractions (AFs) and specific absorbed fractions (SAFs) from electrons were compared with those in the ICRP 1990 model. In the cervical vascular model, electron SAFs from sinusoidal blood in the red bone marrow (RBM) to the target perivascular region were 1.2 to 6.9 times higher than the SAF in the ICRP 1990 model, suggesting an underestimation of the RBM dose. Electrons from the cortical bone source to the perisinusoidal target exhibited energy transfer. The ICRP 1990 model underestimates electron SAFs from radionuclides in sinusoidal blood and cortical bones. A more elaborate model is needed to examine doses for the RBM and effects on hematopoietic and immune functions.