Efficient two-step photocarrier generation in bias-controlled InAs/GaAs quantum dot superlattice intermediate-band solar cells.

We studied the effects of the internal electric field on two-step photocarrier generation in InAs/GaAs quantum dot superlattice (QDSL) intermediate-band solar cells (IBSCs). The external quantum efficiency of QDSL-IBSCs was measured as a function of the internal electric field intensity, and compared with theoretical calculations accounting for interband and intersubband photoexcitations. The extra photocurrent caused by the two-step photoexcitation was maximal for a reversely biased electric field, while the current generated by the interband photoexcitation increased monotonically with increasing electric field intensity. The internal electric field in solar cells separated photogenerated electrons and holes in the superlattice (SL) miniband that played the role of an intermediate band, and the electron lifetime was extended to the microsecond scale, which improved the intersubband transition strength, therefore increasing the two-step photocurrent. There was a trade-off relation between the carrier separation enhancing the two-step photoexcitation and the electric-field-induced carrier escape from QDSLs. These results validate that long-lifetime electrons are key to maximising the two-step photocarrier generation in QDSL-IBSCs.

Gallbladder disease: appearance of associated transient increased attenuation in the liver at biphasic, contrast-enhanced dynamic CT.

PURPOSE: To evaluate the frequency, location, and appearance of transient increased attenuation in the liver during arterial-phase helical or incremental computed tomography (CT) in patients with gallbladder disease without hepatic extension. MATERIALS AND METHODS: Findings in dynamic CT examinations in 31 patients with surgically proved gallbladder disease not extending into the liver and in 31 control patients without gallbladder disease were retrospectively reviewed and correlated with findings in other imaging examinations. RESULTS: Areas of transient increased hepatic attenuation (n = 27) were identified in 22 of 31 patients with gallbladder disease and in only one of 31 control patients. The difference in these findings was statistically significant (P < .001). In the 27 areas of transient increased hepatic attenuation, these findings were categorized as curvilinear or nodular attenuation adjacent to the gallbladder fossa in 13 (48%), segmental or subsegmental attenuation in segment IV and/or V in seven (26%), lobar attenuation in the left lobe (segments II-IV) in four (15%), and nodular attenuation seen as an early enhancing "pseudolesion" in segment IV in three (11%). Hepatic angiography performed in 10 of the 22 patients showed early depiction of the dilated cystic vein (n = 8) and direct communication with the portal branches (n = 2). CONCLUSION: Transient increased attenuation in the liver had a variable appearance at dynamic arterial-phase CT in most patients with gallbladder disease. This attenuation was most likely due to increased blood flow from the hepatobiliary system.

CT of acquired abnormalities of the portal venous system.

Computed tomography (CT), including biphasic contrast material-enhanced helical dynamic scanning and three-dimensional CT angiography, is useful in evaluating acquired abnormalities of the portal venous system. At contrast-enhanced CT, portal venous thrombus usually manifests as low-attenuation intraluminal lesions combined with enlargement of the affected portal vein. Cavernous transformation, a masslike network of intertwined veins that provides an alternative pathway for a stenosed or occluded portal vein, is depicted as multiple, periportal vascular structures. At helical dynamic CT, arterioportal shunts manifest as early enhancement of the affected portal vein, transient hyperperfusion abnormalities with lobar or segmental distribution, or transient wedge-shaped enhancement peripheral to the tumor. In patients with portosplenic venous invasion by malignant neoplasms, peripancreatic or perigastric veins may dilate if they function as hepatopetal collateral veins. In patients with portal hypertension, a variety of hepatofugal collateral pathways can develop, including esophageal, paraesophageal, coronary gastric, inferior phrenic, paraumbilical, abdominal wall, splenorenal, gastrorenal, retrocaval, and mesocaval collateral pathways. An understanding of the varied CT appearances of acquired abnormalities of the portal venous system will allow more definitive diagnosis and help avoid false diagnosis of disease.

Liver neoplasms: diagnostic pitfalls in cross-sectional imaging.

The appearances of most common liver neoplasms at computed tomography (CT) and magnetic resonance (MR) imaging have been established. However, there are considerable overlaps in the appearances of various pathologic entities. Certain hepatic lesions, such as hepatic hemangioma, adenoma, focal nodular hyperplasia, intrahepatic cholangiocarcinoma, metastases, hepatocellular carcinoma, regenerative nodules, adenomatous hyperplastic nodules, abscess, and hepatocellular carcinoma treated with transcatheter arterial chemoembolization, can have unusual characteristics at CT and MR imaging that may lead to misinterpretation. Dynamic helical CT and double-phase multisection dynamic MR imaging techniques may be helpful in differentiating between these entities because hemodynamics of the lesion can be evaluated by obtaining both arterial-phase and delayed-phase images. It is important for radiologists to be aware of these uncommon appearances of liver neoplasms. Familiarity with these varied CT and MR imaging features will permit a more accurate diagnosis and aid in avoidance of a false diagnosis.

An inhibitor of potentially lethal damage (PLD) repair reduces the frequency of gamma-ray-induced mutations in cultured Chinese hamster V79 cells.

Cordycepin (3'-deoxyadenosine, 3'-dA) is an RNA antimetabolite and a radiosensitizer in cultured mammalian cells. In the present paper, the effects of 3'-dA on gamma-ray-induced lethality and 6-thioguanine (6TG)-resistant mutations in cultured Chinese hamster V79 cells were examined. 3'-dA had the effect of sensitizing the lethality induced by gamma-rays. The potentially lethal damage (PLD) repair produced by post-incubation of cells in Hanks' solution after gamma-irradiation was almost completely suppressed by 5 x 10(-5) M 3'-dA. When cells were irradiated with 10 Gy gamma-rays and incubated with 3'-dA for 5 h, the frequency of 6TG-resistant mutations induced by gamma-rays decreased to one-sixth of that of irradiated cells incubated without 3'-dA. The decrease in the frequency of gamma-ray-induced mutations was dependent on the length of incubation time with 3'-dA. It is suggested that the inhibition of PLD repair by 3'-dA may be that of error-prone repair.

Antimutagenic action of cobaltous chloride on radiation-induced mutations in cultured Chinese hamster cells.

The effects of cobaltous chloride on 8-azaguanine (8AG)-resistant mutations induced by gamma-rays or ultraviolet (UV) light in cultured Chinese hamster V79 cells were examined. Cobaltous chloride alone had no significant effects on survival and mutations of V79 cells at concentrations less than 1 x 10(-5) M. Cobaltous chloride at a concentration of 3 x 10(-6) M had a marked effect in reducing 8AG-resistant mutations induced by gamma-rays of 2-6 Gy, when cells were incubated for 6-7 days in the presence of cobaltous chloride after gamma-ray irradiation (posttreatment). The pretreatment of cells with cobaltous chloride for 6 days before gamma-ray irradiation reduced 8AG-resistant mutations induced by gamma-rays. Pre- or post-treatment with cobaltous chloride had no such effect on UV-induced mutations, however. The difference in responsiveness to cobaltous chloride between bacterial and mammalian cell systems is discussed.

Crude tea extracts decrease the mutagenic activity of N-methyl-N'-nitro-N-nitrosoguanidine in vitro and in intragastric tract of rats.

The effects of tea extracts and their ingredients, catechins and L-ascorbic acid (AsA), on the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were examined in vitro and in the stomachs of rats using E. coli WP2 and S. typhimurium TA100. The extracts of green tea and black tea leaves decreased the mutagenic activity of MNNG to E. coli WP2 in vitro in a desmutagenic manner. Catechins such as (-)-epigallocatechin from green tea leaves and the low-molecular-weight tannin fraction isolated from black tea extract with HP-20 resin also exhibited inhibitory effects against the mutagenic activity of MNNG. A desmutagenic effect of AsA on MNNG-induced mutagenicity was observed depending on the dose, though it was complicated. The effects were also demonstrated in the stomachs of rats by assaying the bacterial mutagenic in vitro; the tea extracts previously given orally to rats reduced the mutagenic activity of MNNG remarkably, though simultaneous administration showed less effect. The effectiveness of tea extracts for the decrease of MNNG-induced mutagenesis in vitro and in vivo suggests that the habitual drinking of tea may reduce the tumor-initiating potency of MNNG-type nitrosoureido compounds if they are formed in the stomach.

Adsorption of mutagens by refined corn bran.

Refined corn bran (RCB), a dietary fiber derived from the mechanical refining of corn hulls, effectively adsorbed various environmental mutagens. When RCB was added at a concentration of 10 mg/ml to an aqueous solution of dinitropyrene (DNP), 91.6% of the mutagenicity towards Salmonella tester strain TA98 disappeared. Under similar conditions decreases in mutagenicity of DNP using wheat bran and cellulose powder were 58.4% and 43.0%, respectively. The adsorption of DNP to the fibers appeared irreversible since little mutagenicity was recovered by washing the treated fibers with aqueous buffer solutions of various pHs. Even with an organic solvent (methanol: ammonium hydroxide 50:1), only 2/3 of the mutagenicity of DNP was recovered. RCB could similarly adsorb mutagenic heterocyclic amines such as IQ, Trp-P-1, Trp-P-2, Glu-P-1, and Glu-P-2.

Antimutagenic properties of lactic acid-cultured milk on chemical and fecal mutagens.

The antimutagenic properties of milk cultured with Lactobacillus bulgaricus and Streptococcus thermophilus were examined using streptomycin-dependent strains of Salmonella in an in vitro assay system. The mutagens utilized for testing included 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide, 4-nitroquinoline-N-oxide, and fecal mutagenic extracts from cats, monkeys, dogs, and other mammals. Both types of cultured milk exhibited antimutagenic activity on all mutagens used. Antimutagenic activities of the cultured milks with 2-(2-furyl)-3-(5-nitro-2-furyl) acrylamide and 4-nitroquinoline-N-oxide increased with incubation time but were thermolabile beyond 55 degrees C for 10 min.

Effect of DNA-damaging agents on isolated spleen cells and lung fibroblasts from the mouse mutant "wasted," a putative animal model for ataxia-telangiectasia.

Spleen cells from control and wasted (wst) mice, a putative animal model for the human genetic disease ataxia-telangiectasia, were tested for inhibition of replicative (semiconservative) DNA synthesis after treatments with bleomycin, gamma-irradiation, 4-nitroquinoline 1-oxide, and ultraviolet irradiation. The wasted cells were found to be more resistant than control cells to the first three treatments, but equally sensitive to ultraviolet light. Bleomycin-stimulated repair synthesis in spleen cells was also studied by the CsCl/bromodeoxyuridine method and found to be similar in cells from wasted and control animals. Similarly, no differences in sensitivity to killing by gamma-rays, as manifested by relative cloning efficiencies, were demonstrated between primary lung fibroblasts from mutant and control mice. We concluded that observed defects in DNA repair in wasted cells are not identical to those reported in human cells from ataxia-telangiectasia patients.

Evaluation of the mouse mutant "wasted" as an animal model for ataxia telangiectasia. I. Age-dependent and tissue-specific effects.

The wasted mouse, an animal model proposed for the genetically transmitted human disease ataxia telangiectasia (AT), was examined for its biological, cytogenetic and biochemical properties. In affected homozygotes, a marked age-dependent decrease in the ratio of spleen and thymus to body weight, and a slight but significant decrease in the liver to body weight ratio were observed while no such change was found in the kidney. An age-dependent increase was observed in the frequency of both spontaneous and gamma-ray-induced chromosomal aberrations in bone marrow cells of wasted mice. In littermate control mice, neither of these alterations was observed in an age-dependent manner. The activity of a primer activating enzyme, which has been reported to be deficient in AT cells, also decreased with age in spleen cells, but not in liver cells of affected mice. However, alterations in apurinic DNA endonuclease activity were not detected in the developmental stages examined. These data indicate that this mouse mutant may serve as a useful animal model for studying the relationships between DNA repair and lymphoid tissue differentiation.

Results of the rec-assay of nitropyrenes in the Bacillus subtilis test system.

The rec-assay of the nitropyrenes in Bacillus subtilis was performed. All nitropyrene derivatives were positive in this system. Especially, 3 isomers of 1,3-, 1,6- and 1,8-dinitropyrene and 4-nitropyrene were found to possess strong DNA-damaging capacities at extremely low concentrations.

The pyrogallol related compounds reduce UV-induced mutations in Escherichia coli B/r WP2.

Plant components with bio-antimutagenic activity were screened on UVC (254 nm)-induced mutagenesis using E. coli B/r WP2. The components with a pyrogallol moiety including gallic acid, (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) reduced the mutation induction, but other components such as caffeic acid, chlorogenic acid and quercetin did not. The above compounds with a pyrogallol moiety were also effective on UVAB (295-400 nm)-induced mutagenesis, while they showed little effect on N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced mutagenesis. As this bio-antimutagenic effect was not seen in the DNA excision-repair-deficient strains WP2s and ZA159, the activity by the above plant components might be based on the promotion of the excision-repair system in E. coli B/r WP2.