bluuebunny/crossref_metadata_2025 huggingface dataset:
People and volcanoes: Taal Island, Philippines
Authors: OPPENHEIMER CLIVE
Published: January 2008

Many of the world's most dangerous volcanoes are located in developing countries, which often lack resources for adequate hazard mitigation efforts. Despite technological advances in volcano monitoring, the increasing populations that crowd fertile ash slopes exacerbate the threat of future major volcanic disasters.
Evidence for plant‐arthropod interactions in the fossil record
Authors: SCOTT ANDREW C.
Published: January 2008

From a study of extant arthropods (particularly insects) and plants it is clear that there are many close interactions between the two groups, which must have co‐evolved over a considerable period of time. Surprisingly, the fossil record of such interactions has hardly been studied and has therefore often been assumed to be non‐existent. Interactions include feeding (e.g. leaf and spore/pollen feeding, leaf mining and wood boring), shelter (e.g. the formation of galls), transport, and reproduction (flower pollination). There is fossil evidence for all of these interactions from the time that arthropods and plants first colonized the land. The shortage of data results from lack of study rather than a real absence of interactions.
Geochemistry characterizes provenance in southern Scotland
Authors: STONE P. , GREEN P. M. , LINTERN B. C. , PLANT J. A. , SIMPSON P. R. , BREWARD N.
Published: January 2008

An understanding of the Ordovician—Silurian development of the Southern Uplands accretionary thrust belt is an essential precursor to reconstructing the British sector of the Appalachian—Caledonian orogen. The British Geological Survey (BGS) has now extended its regional geochemical database to cover this controversial area. Integration of the new geochemical data with results from the current geological resurvey allows fresh insights into the provenance patterns of the Southern Uplands' greywacke sequences and constrains the extrapolation of geological boundaries.
Fossil charcoal: a plant‐fossil record preserved by fire
Authors: SCOTT ANDREW C. , JONES TIMOTHY P.
Published: January 2008

Small pieces of black organic material are common in many post‐Devonian sequences, both sedimentary and volcanic. While many of these are coalified plant fragments, others are fossil charcoal, also known as fusain. Charcoalification preserves exquisite detail of the plant ultra‐structure and is best viewed by scanning electron microscopy.
Shaping the eastern Mediterranean coast by earthquakes: Lebanon
Authors: KHAWLIE M. R.
Published: January 2008

Earthquakes in Lebanon's past imply danger in the future.
Exeter: the geology of a cathedral
Authors: DOVE JANE
Published: January 2008

Cathedrals are geologically fascinating and that of Exeter is no exception. Outward appearances are deceptive; although the outer medieval walls are made of Greensand, the core is made of local Permian breccia and volcanics. Beer Stone is used less extensively than generally supposed, although it is important for carving. Nineteenth‐century improvements in transport encouraged greater use of Cotswold and East Midland oolites for the cathedral repairs. Over time, these and local stones have weathered differentially, which has encouraged masons to return to Greensand for very recent repairs.
The geology of Ascension Island
Authors: ROSENBAUM M. S.
Published: January 2008

Ascension Island became famous ten years ago as a staging post for the British Forces in the build up to the Falklands conflict. But whereas the Falkland Islands received considerable media coverage, including in the geological press, this remote island near the Mid‐Atlantic Ridge has until now escaped, although it is a classic example of a Strombolian‐style volcanic pile of alkali‐series basalts and derived volcanic rocks.
Borings and bioerosion in fossils
Authors: PALMER TIM , PLEWES CARYL
Published: January 2008

Ancient marine organisms that excavated holes in shells and other calcium carbonate substrates on the sea bed have not been widely studied by palaeontologists. Together with scrape and scratch marks made by rasping grazers on shell surfaces, they constitute a group of hard–substrate trace fossils that have many modern equivalents. Even the smallest forms can be studied by casting the holes in plastic resin and dissolving the shell. The variety of borers increased in the Mesozoic Era, thereby avoiding the attentions of predatory groups that were radiating at the same time.
Impact in the Caribbean and death of the dinosaurs
Authors: BENTON MICHAEL J. , LITTLE CRISPIN T. S.
Published: January 2008

New work on the 65‐million‐year‐old Chicxulub crater in Mexico shows how giant impacts on Earth occurred. The geological evidence for the aftermath of the impact is currently hotly debated.
Fire and water
Authors: FRANCIS PETER
Published: January 2008

How a new volcanic island failed to change geography, but did change science.
The Navajo Sandstone
Authors: VERLANDER JONATHAN E.
Published: January 2008

The Navajo Sandstone is the remnant of an early Jurassic (Pliensbachian‐Toarcian) aeolian (wind‐blown) system that stretched over most of the western United States for several million years. Interpretation of these deposits suggests that the Navajo erg (sand sea) was one of the most extensive desert systems ever to have existed in the history of the Earth, and probably contained the largest sand dunes that have ever moved across the surface of the planet.
The lost world of the olenid trilobites
Authors: & EUAN N. K. CLARKSON , TAYLOR CECILIA M.
Published: January 2008

Trilobites of the Family Olenidae (Upper Cambrian to Upper Ordovidan) were closely tied to an oxygen‐poor environment. They show a remarkable range of adaptations, testifying to a singular evolutionary plasticity.
THE WAVELENGTH‐DEPENDENT FRACTION OF BIOLOGICAL DAMAGE DUE TO THYMINE DIMERS AND TO OTHER TYPES OF LESION IN ULTRAVIOLET‐IRRADIATED DNA
Authors: Setlow Jane K.
Published: January 2008

Abstract— The sensitivity of Hemophilus influenzae transforming DNA to monochromatic ultraviolet radiation has been determined with and without maximum photoreactivation. The fraction of ultraviolet damage which is photoreactivable (the photoreactivable sector) is large and varies with the wavelengths of the inactivating radiation, decreasing at the extremes of the ultraviolet spectrum. Equating photoreactivable damage with thymine dimer damage, we may interpret the wavelength dependence of photoreactivability and the spectrum for non‐photo‐reactivable damage in terms of the absorption spectra of thymidine and cytosine deoxyriboside. The data suggest that cytosine deoxyriboside alteration is important in non‐photoreactivable biological damage.
SOME ASPECTS OF THE TRIPLET*
Authors: McGlynn S. P. , Smith F. J. , Cilento G.
Published: January 2008

Summary A discussion of certain aspects of triplet state phenomenology which may be of interest to biologists is presented. Particular emphasis is placed on S ‐ T intervals and the interpretation thereof. An attempt is made to relate the size of these intervals to the extent of diradical nature of the triplet state. Spin‐orbital coupling is discussed in a primitive fashion which it is felt leads to much physical insight. External and internal heavy‐atom effects are reviewed and a series of rules relating to the extent to which one might expect a given state of a given compound to be spin‐orbitally coupled are outlined. Finally an attempt is made to analyse objectively some triplet state phenomena and their intervention in biological processes.
THE IONIZATION OF ORGANIC MOLECULAR CRYSTALS BY NEAR U.V. LIGHT*
Authors: Kearns David R.
Published: January 2008

Summary The niechanisms by which near u.v. light cause internal ionization in organic molecular crystals are examined theoretically for the anthracene crystal. Theoretical predictions of the quantum yield for photoionization by the various mechanisms are presented and compared with values recently obtained from studies of photoconduction in anthracene. From this comparison we conclude that:

(i) Good agreement between calculated and observed quantum yields suggests that the method used for the calculations is essentially valid.

(ii) Provided the energy requirements can be met, quantum yields for photoionization may approach unity.

(iii) The lifetimes of excited singlet and triplet states and the rate of intersystem crossing materially influence the quantum yields for photoionization.

(iv) An aggregated, but not necessarily ordered, molecular system should be capable of exhibiting quantum yields for photoionization which are as large as those which can be obtained with single crystals. The possible relevance of these results for biological systems is discussed briefly.
ORGANIC PHOTOCHEMISTRY OF NUCLEIC ACIDS*
Authors: Wacker A. , Dellweg H. , Träger L. , Kornhauser A. , Lodemann E. , Türck G. , Selzer R. , Chandra P. , Ishimoto M.
Published: January 2008

Summary Starting with the isolation of thymine dimer derived from DNA of u.v.‐irradiated bacteria, a systematic investigation was begun from which it was concluded that the basis for the action of u.v.‐light is a photochemical dimerization. Depending on the dose of u.v.‐light and the conditions for hydrolysis of DNA and isolation procedures, other photoproducts of thymine were isolated. Experimental data for the conversion of cytosine to uracil are presented. By use of monochromatic u.v.‐light we could demonstrate that only intrastrand dimerization occurs. The radiation chemical behavior of uracil and cytosine was investigated with tritium labeled compounds.

The mechanism for the various kinds of sensitization with 5‐halogen‐uracils, with dyes (thiopyronin, methylene blue, and pyronin) with carcinogenic hydrocarbons and with furocoumarins, which parallels partly the photochemical degradation of guanine is discussed.

U.V.‐inactivated bacteria and polyuridylic acid are reactivated better by irradiation with visible light when hydrogen peroxide or uranyl acetate are present. The mechanism of this reaction is discussed.

The absence of the α, β‐unsaturated double bond could be expected to protect the thymine molecule from dimerization; after incorporation of azathymine into the DNA, bacteria do indeed exhibit u.v.‐resistance. Moreover, after treatment of bacteria with hydrogen peroxide and visible light, by which the 5,6 double bond in the thymine and cytosine molecules is also attacked, bacteria become u.v.‐resistant.

The specific alteration of uracil and cytosine by u.v.‐irradiation and of guanine through photodynamic action can be used as a simple method for sequence analysis of protein codons. It is also of use in determining the interaction between messenger‐RNA, transfer‐RNA and ribosomes during protein synthesis.
THE MECHANISM FOR FROZEN AQUEOUS SOLUTION IRRADIATION OF PYRIMIDINES*
Authors: Wang Shih Yi
Published: January 2008

Summary Upon freezing an aqueous solution, the formation of crystalline ice forces the solute molecules into solid aggregates. Therefore, identical photodimerimtion of pyrimidines occur in either frozen aqueous solutions or dry solid films. No photodimerization of pyrimidines was evidenced in a homogeneous glycerol glass. Upon freezing an aqueous solution containing solute and a small percentage of organic solvent, the solute molecules together with some organic solvent form ‘puddles’. Therefore, a photochemical reaction in this organic solvent was observed. Only those pyrimidines having an α,β‐unsaturated keto group in their structure undergo photodimerization. The mechanism through which the cyclobutyl ring is formed most probably involves a diradical intermediate. The unstable thymine monohydrate crystal has the most favorable orientation for two thymine molecules to form dimer. Therefore, the photodimerization process for thymine is less favored in dry solid film than in frozen aqueous solution because the thymine monohydrate crystalline lattice collapses under low humidity.
PHOTOREACTIVATION AND PHOTOPROTECTION*
Authors: Jagger John
Published: January 2008

Summary Survival after far ultraviolet irradiation can be greatly increased in most cells by a posttreatment with near ultraviolet or violet‐blue radiation (photoreactivation) or, in some cells, by a pretreatment with near ultraviolet radiation (photoprotection). In addition, many cells recover from some lethal far ultraviolet damage by posttreatments not involving light (dark recovery), and it seems likely that considerable recovery of this type occurs even under ‘normal’ postirradiation conditions that do not involve any special ‘treatments’. In this paper, three aspects of photoreactivation of lethal damage are considered: (1) the nature of photoreactivable damage, including the possibility of cytoplasmic and RNA, as well as DNA, damage; (2) the mechanism of direct (photoenzymatic) photoreactivation, with special reference to dose‐rate saturation and temperance dependence; and (3) relations among photoprotection, dark recovery, and photoreactivation, with particular reference to the phenomenon of ‘indirect photoreactivation’, which is similar in mechanism to photoprotection. The general approach is broad, an attempt being made to point out some gaps and inconsistencies in our knowledge of these phenomena.
PHOTODYNAMIC ACTION*
Authors: Spikes John D. , Glad Blaine W.
Published: January 2008

Summary If trypsin is illuminated with visible light in the presence of an appropriate sensitizing dye and oxygen, a loss of enzymatic activity is observed. This phenomenon is called photodynamic inactivation. Quantum requirement studies were made on this system using illumination provided by a projector or high‐pressure mercury arc light equipped with multilayer interference filters. Light energy absorbed was measured using a vacuum thermocouplegalvanometer combination which was calibrated with a standard lamp. Aliquots of the illuminated system were taken at intervals and the tryptic activity remaining was assayed spectrophotometrically using the benzoyl‐arginine ethyl ester (BAEE) technique. BAEE is a synthetic substrate of trypsin. Two sensitizing dyes were used, methylene blue (MeB) and riboflavin‐5′‐phosphate (FMN). The quantum requirement of inactivation with both sensitizers decreases rapidly with increasing dye concentration, reaches a minimum, and then increases. Both sensitizers show increased quantum requirements of inactivation with increasing enzyme concentration. Both show quantum requirements which are independent of light intensity. FMN‐sensitized photodynamic inactivation shows large quantum requirements at acid pH's and low quantum requirements at basic pH's. MeB shows no activity as a sensitizer at acid pH's and high activity at basic pHs. Quantum requirements decrease slightly from 4°C to 33°C. The two dyes show different efficiencies of utilization of trapped light energy under similar conditions, which suggests that different photodynamic mechanisms may be acting in each case.
THE RMOLUMINESCENCE OF l‐TYROSINE UNDER U.V. IRRADIATION*
Authors: Weissbluth M. , Steele R. E. , Day E. P.
Published: January 2008

Abstract— The thermoluminescence of polycrystalline L‐tyrosine kept at 77°K during irradiation by U.V. light has been investigated. On the basis of action spectra, emission spectra, and decay kinetics, a phenomenological model is proposed in which the final radiative transition is from the lowest triplet to the ground singlet state of the molecule. The role of metal ions in trace amounts, various gases in contact with the sample and a bleaching effect by white light were also studied.
PHOTOLYSIS OF NITRATE ESTERS—II. SOLUTION PHOTOLYSIS OF ARALKYL NITRATE ESTERS: KINETICS, ESR SPECTRA, AND PHOTOPRODUCTS
Authors: Csizmadia I. G. , Hayward L. D.
Published: January 2008

Abstract— Irradiation of benzyl nitrate, meso‐ and dl‐hydrobenzoin dinitrates, and cis‐ and trans‐1,2‐acenaphthenediol dinitrates in benzene solutions 0.02M in nitrato groups at 265–313 mp decomposed the esters with a quantum yield of 0.4±0.2 in reasonable agreement with earlier work on the gas‐phase photolysis of ethyl nitrate. An important primary process was ArRCHONO2+hvArRCHO +NO2, although ArRCHONO2+hvArRCHONO + O was not excluded. In secondary reactions solvent benzene was oxidized and nitrated, aldehydes were formed from the nitrate esters, and nitric oxide was evolved. The higher quantum yields of the photodecomposition in ethanol (0.8±0.3) and ether (3±1) solutions were interpreted in terms of a charge‐transfer state similar to that found with nitroalkanes in these solvents. Acetaldehyde was produced in a rapid secondary reaction in alcohol solutions at 25° and at 77° K, NO2 was identified as an intermediate from the ESR spectrum. No stereospecificity was detected in a comparison of rates, photoproducts, and ESR spectra for the stereoisomers. The overall results indicated inter‐ rather than intramolecular migration of oxy‐nitrogen groups in secondary reactions. An apparently new, long‐lived, oxynitrogen radical was detected in benzene solutions of nitric oxide and nitrate esters irradiated at 25°.
PHOTOREACTIVATION OF CLOVER YELLOW MOSAIC VIRUS
Authors: Chessin Meyer
Published: January 2008

Abstract— Clover yellow mosaic virus, in common with other plant viruses with flexuous, rod‐like particles, can be photoreactivated. At lower U.V. doses, photoreactivation is masked by an inhibitory effect on virus infection of visible light alone.
A METHOD OF ASSAYING IN VIVO THE SURVIVAL OF ULTRA VIOLET‐IRRADIATED TUMOUR CELLS
Authors: Stevens G. H. , Roe E. M. F.
Published: January 2008

Abstract— The growth of ultraviolet‐irradiated ascites tumour cells in adult animals which have received a total‐body dose of x‐radiation appears to be a suitable method to obtain data on the survival of the treated tumour cells, if the dose of total‐body radiation and its time before tumour cell inoculation are chosen correctly.

In assessing tumour cell survival, the analysis of the time of appearance of the resulting solid tumours, using the linear relationship between the reciprocal of this time and the logarithm of the number of cells injected is preferred to probit or to Reed‐Muench analysis of the number of tumour‐takes. The 1/T method of analysis yields more precise estimates of the survival ratios and greater economy in the use of host animals without a disproportionate increase in the labour involved in obtaining the data.

An application of this method to the determination of survival‐ratios of u.v.‐irradiated Landschütz ascites tumour cells is described.
THE EFFECTS OF ULTRAVIOLET AND VISIBLE RADIATION ON MOUSE ASCITES TUMOUR CELLS
Authors: Roe E. M. F. , Stevens G. H.
Published: January 2008

Abstract— Effects of ultraviolet and visible radiation on the viability of Landschutz ascites tumour cells have been tested by growing control and treated tumour samples in adult mice. The tumour cells were irradiated as a dilute suspension in isotonic buffered salt solution, and were equilibrated at 0°C with oxygen or with nitrogen before irradiation.

Tumour cell proliferation was measured by a variety of techniques. The preferred assay‐method was the growth of solid tumours in the axillae and groins of mice after sub‐cutaneous inoculation of varying dilutions of treated or control ascites tumour cells. The immune response of the mice to the injected cells was reduced by whole body irradiation with a 300r dose of x‐rays two days before inoculation. Results were calculated from parallel line assays using the reciprocal of the delay in appearance of the solid tumours up to 30 days post‐innoculation. This reciprocal (1/T) was linearly related to the logarithm of the number of cells inoculated.

Photoreactivation has been demonstrated for this system, in which both U.V. and visible radiations were absorbed by the same cells. Light delivered alone in oxygen or in nitrogen was without effect on cell‐viability, but it increased cell‐survival after u.v.‐irradiation in nitrogen and decreased survival after u.v.‐irradiation in oxygen. Ultraviolet radiation alone was not significantly more lethal in oxygen than in nitrogen. A further observation in this work was an interaction between irradiated and control tumour cells injected into the same animal.

It is suggested that the radiation used may affect the antigenic character of the tumour cells as well as their reproductive capadity.
A STUDY OF CHLOROPHYLL FLUORESCENCE IN VIVO BY A FLOW METHOD
Authors: Lavorel Jean
Published: January 2008

Abstract— A flow method has been devised for the study of fluorescence transients during the induction period of photosynthetic systems. The principle of transformation of time‐transients into space‐transients is quantitatively worked out and the characteristics and mode of operation of the apparatus is described and illustrated with experimental results.

With this method spectroscopic and kinetic investigation of in vivo chlorophyll fluorescence have been undertaken. The fluorescence emission can be split into two componmts—a variable part and a constant part—with different spectral distributions. The excitation spectrum of the light induced fluorescence changes shows that the variable part is sensitized by system 11, whereas the constant part mainly sensitized by system II has a small component originating from system I. The light‐induced fluorescence change decays in darkness with half‐time of about 10‐2s; this decay is highly sensitive to the action of inhibitors of oxygen evolution.

The flow method can be extended to measurements of oxygen, luminescence, absorption differences. It permits using high‐intensity analytic beams with no actinic action; it is well suited for the integration of low level signals.
SOME RELATIONSHIPS BETWEEN STRUCTURE AND CHEMILUMINESCENCE IN TRIPHENYLIMIDAZOLES*
Authors: Philbrook G. E. , Maxwell M. A. , Taylor R. E. , Totter J. R.
Published: January 2008

Abstract— Lophine (2, 4, 5‐triphenylimidazole) and sixteen of its derivatives bearing substituents in the 2‐phenyl group have been synthesized and characterized. The fluorescence excitation and emission spectra in neutral and basic solution in 70% dimethylsulfoxide‐30 % water have been determined. The chemiluminescent intensities in 70% DMSO‐30% water, 0.33 N in NaOH have been measured. The maximum chemiluminescent emission wavelength was found to fall at 530 mμ for all compounds except the nitro derivatives whose intensities were too low to measure. The compounds bearing substituents in the meta and/or para positions of the 2‐phenyl group give linear Hammett plots. The value of p is —1.96 + 0.06. The constant emission wavelength and linear Hammett relation is interpreted in terms of the same mechanism and emitting species for all the compounds studied.
SOME OBSERVATIONS ON THE PROPERTIES OF CRYSTALLINE BACTERIAL LUCIFERASE*
Authors: Cormier Milton J. , Kuwabara Seishi
Published: January 2008

Abstract— We describe a number of properties of our crystalline bacterial luciferase preparations, such as absorption spectra and fluorescence characteristics which are not typical of flavoproteins. Acid extraction of the enzyme or digestion with proteolytic enzymes do not lead to the liberation of flavin‐like compounds, as judged by fluorescence techniques. Other dyes such as reduced neutral red will replace FMNH2 in this system, and irradiation of the enzyme with u.v. light does not change the ratio of light production with FMNH2 and reduced neutral red. Thus, all efforts to detect flavin in our enzyme have failed, suggesting that FMN is not necessarily involved in the emitting complex. It is of interest that addition of hydrosulfite to luciferase solutions shifts the fluorescence emission to the blue and thus close to that of bioluminescence emission. Separations of two different FMN‐dependent DPNH oxidases are described, one of which is closely associated with luciferase and exhibits both DPNH and TPNH oxidase activity.
KINETIC STUDIES TO INTERPRET ‘HIGH‐ENERGY PHENOMENA’ OF PHOTOMORPHOGENESISL ON THE BASIS OF PHYTOCHROME
Authors: Wagner E. , Mohr H.
Published: January 2008

Abstract— Kinetic studies with the mustard seedling (Sinapis alba L.) support the hypothesis that the so‐called ‘high energy reaction’ of photomorphogenesis can be understood solely on the basis of phytochrome. Light‐induced anthocyanin synthesis (a typical ‘positive’ photoresponse(1) and light dependent inhibition of hypocotyl lengthening (a typical ‘negative’ photoresponse(1)) have been investigated. In order to explain the experimental data we have to assume that there are two different types of phytochrome 730 which differ greatly as far as their resistance to irreversible destruction is concerned. The existence of these two different types of phytochrome 730 has already been postulated on the basis of spectrophotometric measurements in vivo.(2)
ON PHYTOCHROME AND CYTOCHROMES IN PHOTOPERIODIC PHENOMENA: A BIOCHEMICAL APPROACH
Authors: Greef J. A. De
Published: January 2008

Réumé— Pour les plantes vertes nous présentons une hypothèse alternative en ce qui concerne l'action de rayons de longueur d'onde donnée sur la morphogénèse. Sur la base de données analytiques le chloroplaste peut être considéré comme similaire à la mitochondrie, avec la réserve importante que des composés photoactifs participent aux oxydations chimiques terminales dans le chloroplaste. Dans les plantes vertes deux cytochromes sont connus: un du type c, le cytochrome f, et un autre de type b6 le cytochrome b6. On a proposé que le cytochrome b6 est réduit et que l'eau est oxydée simultanément. L'électron libéré est transféré sur le cytochrome f qui, ensuite, est oxydé tandis que le NADP est réduit. De plus, la lumière rouge foncé paraît convertir le cytochrome b6 dans la forme oxydée. Celle‐ci peut passer à nouveau dans la forme reduite après élairement sous rayons de longueur d'onde plus courte. Le cytochrome b6 pourrait donc occuper une position de commutateur entre les systèmes oxydés et réduits dans la cellule. Déterminant pour la position de ce commutateur sont d'une part la longueur d'onde de la lumière et d'autre part la cwantité totale d'énérgie.

Le fait aue le cvtochrome b6 est maintenu uar la lumière rouge‐foncé dans la forme oxvdée. empêherait la réduction de NADP. Ainsi ia voie métaboliGe normale serait modifiée ce qui trouverait son expression dans un changement de l'aspect morphologique de la plante.

L'analogie est très remarquable entre le spectre d'action de la forme oxydée du cytochrome b6 et celui de la forme P660 du phytochrome qui se forme également suite à un éclairement rouge‐foncé et qui est considerée comme physiologiquement inactive. Plusiers données expérimentales soutiennent ce point de vue.
KINETIC BEHAVIOR OF EPR SIGNAL I: INDUCTION EFFECTS IN INTACT ALGAE
Authors: Weaver Ellen C.
Published: January 2008

Abstract— There is considerable evidence that the light‐induced narrow EPR signal I at g= 2·0025 in green algae is a reflection of the turnover of the photosynthetic reaction center, P700. A lag period or induction effect of the formation of this signal, subsequent to a dark period in whole fresh cells, is similar to induction effects for the bleaching of P700. The rate of formation of the signal is slower the longer the preceding dark period. DCMU does not much affect the induction phenomenon, but heating the cells to 60° abolishes it. Some substance or process which exists in the intact cell is altered by light and is detectable by its effect on signal I and on the rate of light‐induced oxidation of P700 and cytochrome.
TECHNIQUES OF FLASH PHOTOLYSIS*
Authors: Boag John W.
Published: January 2008

Abstract— The design of a typical flash photolysis equipment is considered in detail and the factors limiting the time resolution and the sensitivity are analyzed. The characteristics of low pressure discharge lamps are compared with those of high pressure arcs, of exploding foils and of the electromagnetic ‘pinch’ discharge. For the analytical flash, operating at a much lower power level, many satisfactory designs exist which give a good continuum and short duration. Methods of improving the optical system are discussed, and the special advantages of using a microscope optical system for investigating substances with high extinction coefficients are illustrated by an account of recent work on chlorophyll.
SOME QUALITATIVE DIFFERENCES BETWEEN GROUND AND EXCITED STATES
Authors: MALRIEU J. P.
Published: January 2008

Abstract— Electronic excitation is deiocalized, particularly in conjugated systems: the language of molecular orbitals (MO), already very useful for ground‐state properties, is absolutely necessary to explain excited‐state properties. But the theoretical representation of excited states has special difficulties. Approximations used to represent excited states are: (1) Single determinant wave‐functions, built with the ground‐state MO (Hückel or SCF) or with special MO (restricted or unrestricted Hartree–Fock). (2) A configuration interaction: studied by perturbation development. (3) The excitonic treatment, i.e. interaction of localized excitations. The theory is applied to saturated molecules.

The stable geometry of the excited state is different from that of the ground state and plays a role in many physical observables (dipole moment, vibrational structure of the band, lifetime) and in chemical processes.

La excitación electrónica está deslocalizada particularmente en sistemas conjugados. El lenguaje de los orbitales moleculares (MO) que ha sido muy util para aclarar las propiedades del estado fundamental es absolumente necesario para explicar las propiedades del estado excitado. Pero la representación teórica de los estados excitados presenta algunas dificultades. Las aproximaciones usadas para representar los estados excitados son: (1) funciones de onda con un solo determinante construidas con el orbital molecular del estado fundamental (Hückel o SCF) o con el orbital molecular particular (restringido o no restringido Hartree‐Fock), (2) una configuration de la interacción estudiada por métodos de perturbación, (3) el tratami‐miento “excitonic”, es decir interaction de las excitaciones localizadas. La teoría se aplica a moleculas saturadas. La geometría estable del estado excitado es diferente a la del estado fundamental y tiene un rol importante en muchas de las propiedades fisicas observables, (momento dipolar, estructura vibrational y vida media) y en los procesos quimicos.
LUMINESCENCE SPECTRA OF TRANSITION METAL COMPLEXES*
Authors: ZULOAGA F. , KASHA M.
Published: January 2008

Abstract— A systematic quantum mechanical and spectroscopic study has been made for transition metal ions containing d6 atomic configurations. Ligand field parameters and spectral data are summarized. For suitable chelates of Co(III), Rh(III), Ir(III), and Pt(IV), the lowest transition is characterized as being of d–d characteristics, with weak and broad structureless bands. For suitable chelates of Ru(II) and Os(II), the lowest transition is characterized as being of d–aπ characteristics (involving an antibonding orbital of π‐origin in the ligand), with strong bands showing pure ligand vibrational structure. The competitive nature of d–d vs. d–aπ transitions is interpreted for pyridyl chelate of Ir(III) showing d–d lowest transitions and an o‐phenanthroline chelate of Ir(III) reported in the literature as showing d‐aπ transitions. A general quantum‐theoretical rule for chelates of transition metal ions is given, and the application of the results to photochemistry and radiation chemistry is indicated.

Se ha efectuado un estudio mecánico cuántico y espectroscópico para la transición de iones metálicos que contienen una configuración atómica d6. Para quelatos apropiados de Co(III). Rh(III), Ir(III) y Pt(IV) la transición más baja está representada como una caracteróstica d–d con bandas débiles y poco estructuradas. Para quelatos apropiados de Ru(III) y Os(II) la transición mas baja está representada como una característica d–aπ (involucrando un orbital de antiunión de origen π en el ligante). con bandas fuertes mostrando la estructura vibracional del ligante. La naturaleza competitiva de las transiciones d–d vs. d–dπ es interpretada para quelatos de piridilo de Ir(III) mostrando la más baja transición d–d, y para un quelato de o‐fenentrolina de Ir(III) que tiene transiciones d–aπ segun ha sido comunicado en la literatura. Se da una regla general teorético—cuántica para quelatos de transición de iones metálicos, y se indica la aplicación de los resultados afotoquímica y radiación química.
HEAVY ATOM PERTURBATION IN MOLECULES RELATED TO THYROXINE
Authors: CILENTO G. , SANIOTO D. L. , ZINNER K. , BERENHOLC M.
Published: January 2008

En conección con la perturbación producida en las hormonas tiroideas y moléculas asociadas, por el átomo pesado iodo; se ha investigado el espectro de absorción singulete‐triplete de la p—benzoquinona (max = 539 nm) cuando se la sustituye en la posicién 2–6 con el dihalógeno. En oposición a los resultados reportados por Kuboyama, no se observaun cambio en la intensidad cuando se sustituyen dos átomos de cloro. La ausencia de acomplamiento spin‐órbita se ve confirmada por la pequen̂a intensificación de la absorción cuando los átomos sustituidos son bromo o iodo, y probablemente está conectada con el caracter n→π* de la transición. Algo sorpresivamente. la sustitución de dos átomos de iodo produce un marcado efecto batocromico cerca de donde esta localizada la transición singulete‐ triplete, aproximadamente encima de los 600 nm.
PHOTOCHEMISTRY OF POLYNUCLEOTIDES: A SUMMARY OF TEMPERATURE EFFECTS*
Authors: RAHN R. O. , HOSSZU J. L.
Published: January 2008

Abstract— The photochemistry of polynucleotides is strongly dependent upon the temperature at which the irradiation is done. At 77°K only a limited number of pyrimidines undergo dimerization. Hydration and interstrand cross‐linking is completely prevented at this temperature. Irradiation at low temperatures leads to the formación in DNA of the spore‐type photoproduct. At elevated temperatures destacking of the bases, which occurs upon melting, leads to lower dimer yields. Variation of the irradiation temperature has proven to be of great value in determining the biological effectiveness of photoproducts that differ in their temperature dependence.

La fotoquímica de los polinucleótidos observa una marcada dependencia con la temperatura a la que se efectua la radiación. A 77°K solo un numero limitado de pirimidinas sufre dimerización. La hidratación se puede prevenir completamente a esta temperatura. Bajas temperaturas conducen a la formación de un foto‐producto similar al de las esporas, fenómeno que no ocurre a 298°K. A elevadas temperaturas por encima del punto de fusión, se obtienen rendimientos bajos en dímeros. La variación de la temperatura de irradiación se ha probado que es de gran valor en la determinación de la efectividad biológica de los fotoproductos que difieren en su dependencia con la temperatura.
RADIOLYSIS OF PEPTIDES AND PROTEINS
Authors: WHEELER OWEN H.
Published: January 2008

Abstract— A considerable amount of research has been published on the effect of ionizing radiation on amino acids. In aqueous solution the products are formed from an intermediate radical resulting from the abstraction of a hydrogen atom from the α‐carbon atom. Aromatic amino acids are predominately hydroxylated in the ring, phenylalanine forming tyrosine and tyrosine affording dihydroxylphenylalanine. The data on proteins are largely concerned with denaturation and the effect of radiation protecting compounds. The few studies on peptides have indicated that the mechanism of their radiolysis is similar to that of amino acids. Recent work indicates that the nature of the amino acid affects the resistance of the peptide linkage. Aromatic rings are also hydroxylated in preference to attack on the peptide group. The products were identified and analyzed using carbon‐14‐labeled peptides. The radiation protection effects of a series of organic compounds have been determined by competition for hydroxyl radicals with the labeled peptide. Comparison is made between the radiolysis and photolysis of peptides.

Una considerable cantidad de datos ha sido publicados sobre el efecto de radiación ionizante en amino‐ácidos. En solución acuosa los productos se forman a partir de un radical intermedio que resulta de la pérdida de un hidrógeno unido al carbono α. Los aminoácidos aromáticos sufren procesos de hidroxilación en el anillo, la fenilalanina formando tirosina y la tirosina formando dihidroxifenilalanina. Los datos sobre proteinas se refieren principalmente a la desnaturalización y al efecto de compuestos que protegen de la radiación. Algunos estudios en péptidos indican que el mecanismo de radiolisis es similar al de los amino‐ácidos. Trabajos recientes indican que la estabilidad de la unión peptidica depende de la naturaleza del aminoácido. Los anillos aromáticos son hidroxilados para luego ser atacada la unión peptídica. Los productos fueron analizados usando péptidos marcados con carbono‐14. Los efectos de protección a la radiación de una serie de compuestos orgánicos nan sido determinados por competencia con radicales OH· usando peptidos marcados. Se efectuan comparaciones entre la radiólisis y lafotólisis de péptidos.
Leakage and scatter radiation from a double scattering based proton beamlinea)
Authors: Moyers M. F. , Benton E. R. , Ghebremedhin A. , Coutrakon G.
Published: January 2008

Proton beams offer several advantages over conventional radiation techniques for treating cancer and other diseases. These advantages might be negated if the leakage and scatter radiation from the beamline and patient are too large. Although the leakage and scatter radiation for the double scattering proton beamlines at the Loma Linda University Proton Treatment Facility were measured during the acceptance testing that occurred in the early 1990s, recent discussions in the radiotherapy community have prompted a reinvestigation of this contribution to the dose equivalent a patient receives. The dose and dose equivalent delivered to a large phantom patient outside a primary proton field were determined using five methods: simulations using Monte Carlo calculations, measurements with silver halide film, measurements with ionization chambers, measurements with rem meters, and measurements with CR‐39 plastic nuclear track detectors. The Monte Carlo dose distribution was calculated in a coronal plane through the simulated patient that coincided with the central axis of the beam. Measurements with the ionization chambers, rem meters, and plastic nuclear track detectors were made at multiple locations within the same coronal plane. Measurements with the film were done in a plane perpendicular to the central axis of the beam and coincident with the surface of the phantom patient. In general, agreement between the five methods was good, but there were some differences. Measurements and simulations also tended to be in agreement with the original acceptance testing measurements and results from similar facilities published in the literature. Simulations illustrated that most of the neutrons entering the patient are produced in the final patient‐specific aperture and precollimator just upstream of the aperture, not in the scattering system. These new results confirm that the dose equivalents received by patients outside the primary proton field from primary particles that leak through the nozzle are below the accepted standards for x‐ray and electron beams. The total dose equivalent outside of the field is similar to that received by patients undergoing treatments with intensity modulated x‐ray therapy. At the center of a patient for a whole course of treatment, the dose equivalent is comparable to that delivered by a single whole‐body XCT scan.
Small fields: Nonequilibrium radiation dosimetry
Authors: Das Indra J. , Ding George X. , Ahnesjö Anders
Published: January 2008

Advances in radiation treatment with beamlet‐based intensity modulation, image‐guided radiation therapy, and stereotactic radiosurgery (including specialized equipments like CyberKnife, Gamma Knife, tomotherapy, and high‐resolution multileaf collimating systems) have resulted in the use of reduced treatment fields to a subcentimeter scale. Compared to the traditional radiotherapy with fields , this can result in significant uncertainty in the accuracy of clinical dosimetry. The dosimetry of small fields is challenging due to nonequilibrium conditions created as a consequence of the secondary electron track lengths and the source size projected through the collimating system that are comparable to the treatment field size. It is further complicated by the prolonged electron tracks in the presence of low‐density inhomogeneities. Also, radiation detectors introduced into such fields usually perturb the level of disequilibrium. Hence, the dosimetric accuracy previously achieved for standard radiotherapy applications is at risk for both absolute and relative dose determination. This article summarizes the present knowledge and gives an insight into the future procedures to handle the nonequilibrium radiation dosimetry problems. It is anticipated that new miniature detectors with controlled perturbations and corrections will be available to meet the demand for accurate measurements. It is also expected that the Monte Carlo techniques will increasingly be used in assessing the accuracy, verification, and calculation of dose, and will aid perturbation calculations of detectors used in small and highly conformal radiation beams.
Effect of x‐ray energy dispersion in digital subtraction imaging at the iodine ‐edge—A Monte Carlo study
Authors: Prino F. , Ceballos C. , Cabal A. , Sarnelli A. , Gambaccini M. , Ramello L.
Published: January 2008

The effect of the energy dispersion of a quasi‐monochromatic x‐ray beam on the performance of a dual‐energy x‐ray imaging system is studied by means of Monte Carlo simulations using MCNPX ( Monte Carlo N‐Particle eXtended) version 2.6.0. In particular, the case of subtraction imaging at the iodine ‐edge, suitable for angiographic imaging application, is investigated. The average energies of the two beams bracketing the iodine ‐edge are set to the values of 31.2 and 35.6 keV corresponding to the ones obtained with a compact source based on a conventional x‐ray tube and a mosaic crystal monochromator. The energy dispersion of the two beams is varied between 0 and 10 keV of full width at half‐maximum (FWHM). The signal and signal‐to‐noise ratio produced in the simulated images by iodine‐filled cavities (simulating patient vessels) drilled in a PMMA phantom are studied as a function of the x‐ray energy dispersion. The obtained results show that, for the considered energy separation of 4.4 keV, no dramatic deterioration of the image quality is observed with increasing x‐ray energy dispersion up to a FWHM of about 2.35 keV. The case of different beam energies is also investigated by means of fast simulations of the phantom absorption.
MOSFET sensitivity dependence on integrated dose from high‐energy photon beams
Authors: Tanyi James A. , Krafft Shane P. , Hagio Tomoe , Fuss Martin , Salter Bill J.
Published: January 2008

The ability of a commercially available dual bias, dual MOSFET dosimetry system to measure therapeutic doses reproducibly throughout its vendor‐defined dose‐based lifetime has been evaluated by characterizing its sensitivity variation to integrated/cumulative doses from high‐energy (6 and 15 MV) photon radiotherapy beams. The variation of sensitivity as a function of total integrated dose was studied for three different dose‐per‐fraction levels; namely, 50, 200, and 1200 cGy/fraction. In standard sensitivity mode (i.e., measurements involving dose‐per‐fraction levels ), the response of the MOSFET system to identical irradiations increased with integrated dose for both energies investigated. Dose measurement reproducibility for the low (i.e., 50 cGy) dose fractions was within (if the system was calibrated before each in‐phantom measurement) and [if the system was calibrated prior to first use, with no intermediate calibration(s)]. Similarly, dose measurement reproducibility was between and for the conventional (i.e., 200 cGy) dose fractions and between and for escalated (i.e., 1200 cGy) dose fractions. The results of this study suggest that, due to the progressively increasing sensitivity resulting from the dual‐MOSFET design, frequent calibrations are required to achieve measurement accuracy of (within one standard deviation).
Surface dosimetry for oblique tangential photon beams: A Monte Carlo simulation study
Authors: Chow James C. L. , Grigorov Grigor N.
Published: January 2008

The effect of beam obliquity on the surface relative dose profiles for the tangential photon beams was studied. The 6 and 15 MV photon beams with and field sizes produced by a Varian 21 EX linear accelerator were used. Phase‐space models of the photon beams were created using Monte Carlo simulations based on the EGSnrc code, and were verified using film measurements. The relative dose profiles in the phantom skin, at 2 mm depth from the surface of the half‐phantom geometry, or HPG, were calculated for increasing gantry angles from 270 to 280 deg clockwise. Relative dose profiles of a full phantom enclosing the whole tangential beam (full phantom geometry, or FPG) were also calculated using Monte Carlo simulation as a control for comparison. The results showed that, although the relative dose profiles in the phantom skin did not change significantly with an oblique beam using a FPG, the surface relative depth dose was increased for the HPG. In the HPG, with 6 MV photon beams and field , when the beam angle, starting from 270 deg, was increased from 1 to 3 deg, the relative depth doses in the phantom skin were increased from to at 10 cm depth. This increase in dose was slightly larger than the dose from 15 MV photon beams with the same field size and beam angles, where the relative depth doses in phantom skin were increased from to at 10 cm depth. A parameter called the percent depth dose (PDD) ratio, defined as the relative depth dose from the HPG to the relative depth dose from the FPG at a given depth along the phantom skin, was used to evaluate the effect of the phantom–air interface. It is found that the PDD ratio increased significantly when the beam angle was changed from zero to 1–3 degrees. Moreover, the PDD ratio, for a given field size, experienced a greater increase for 6 MV than for 15 MV. For the same photon beam energy, the PDD ratio increased more with a field compared to . The results in this study will be useful for physicists and dosimetrists to predict the surface relative dose variations when using clinical tangential‐like photon beams in radiation therapy.