Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997.

The evolution of the Earth's climate has been extensively studied, and a strong link between increases in surface temperatures and greenhouse gases has been established. But this relationship is complicated by several feedback processes-most importantly the hydrological cycle-that are not well understood. Changes in the Earth's greenhouse effect can be detected from variations in the spectrum of outgoing longwave radiation, which is a measure of how the Earth cools to space and carries the imprint of the gases that are responsible for the greenhouse effect. Here we analyse the difference between the spectra of the outgoing longwave radiation of the Earth as measured by orbiting spacecraft in 1970 and 1997. We find differences in the spectra that point to long-term changes in atmospheric CH4, CO2 and O3 as well as CFC-11 and CFC-12. Our results provide direct experimental evidence for a significant increase in the Earth's greenhouse effect that is consistent with concerns over radiative forcing of climate.

Design of an efficient broadband far-infrared Fourier-transform spectrometer.

As part of a feasibility study for a far-infrared Fourier-transform spaceborne spectrometer, the criteria that drive the choice of the instrument configuration have been identified as broadband operation, dual input and output ports, optics of the interferometer with full tilt compensation, and measurement of both planes of polarization of the source on a single detector. Despite the fact that some of these requirements are apparently difficult to reconcile, a new configuration of the polarizing interferometer that meets all the above requirements has been identified. The considerations that led to the design of this new configuration are discussed.

Problems associated with microbiological validation of sterilization by ionizing radiation.

Potential solutions to some of the practical problems experienced when validating products processed by radiation sterilization are discussed in this article. The standards for validation and routine control of radiation sterilization are to be revised next year and there is now an opportunity for the industry to influence the effectiveness of those revisions. Medical device manufacturers are encouraged to make views known to help ensure a simpler standard that is widely implemented.

X-ray evidence that in contracting live frog muscles there exist two distinct populations of myosin heads.

Using synchrotron radiation and whole muscles, 2 ms time-resolved x-ray diffraction patterns were recorded at 8 degrees C. The results show that in both isotonic and isometric contractions, as well as in length changes imposed at maximum tension [Po], the meridional third myosin layer line consists of two distinct reflections with different intensities and spacings that measure approximately 14,623 and 14,412 nm at Po. Although the intensity behavior of the two reflections is strikingly different during quick releases, it is very similar during stretches. Study of the time courses indicates that myosin heads diffracting at Po with the approximately 14.623 nm periodicity are actively involved in tension production. Those diffracting at Po with the periodicity of approximately 14.412 nm appear not be associated with tension production during isometric contraction and releases, but the results suggest that they are recruited during stretches and here contribute to tension production. Our most important conclusion is that under all conditions of contraction we have investigated there exist two populations of myosin heads, each with a well defined axial disposition and configuration.

Using stars for remote sensing of the Earth's stratosphere.

A new UV-visible spectrometer system that measures the absorption of light from stars and planets by constituents in the Earth's atmosphere is described. Because it can be used to make measurements at night, the system has a significant advantage for measuring polar constituents in winter, when conditions that might give rise to ozone loss are initiated. Other advantages arise from the use of a cooled two-dimensional CCD array as the detector: an array detector avoids spectral noise resulting from scintillation of stars or from clouds passing overhead and allows for the possibility of measuring several constituents simultaneously; its second dimension permits auroral light from the atmosphere adjacent to the star to be measured simultaneously and subtracted from the stellar light, and a modern low-noise CCD allows us to use a telescope of modest diameter. The few previous measurements of constituents made by the use of stellar absorption did not have these advantages. The instrument was configured for simplicity and ease of use in field measurements and was deployed outside in winter in Northern Sweden in 1991. Examples of ozone measurements are shown.

Two-dimensional time-resolved X-ray diffraction studies of live isometrically contracting frog sartorius muscle.

Results were obtained from contracting frog muscles by collecting high quality time-resolved, two-dimensional, X-ray diffraction patterns at the British Synchrotron Radiation Source (SERC, Daresbury, Laboratory). The structural transitions associated with isometric tension generation were recorded under conditions in which the three-dimensional order characteristic of the rest state is either present or absent. In both cases, new layer lines appear during tension generation, subsequent to changes from activation events in the thin filaments. Compared with the 'decorated' actin layer lines of the rigor state, the spacings of the new layer lines are similar whereas their intensities differ substantially. We conclude that in contracting muscle an actomyosin complex is formed whose structure is not like that in rigor, although it is possible that the interacting sites are the same. Transition from rest to plateau of tension is accompanied by approximately 1.6% increase in the axial spacing of the myosin layer lines. This is explained as arising from axial disposition of the interacting myosin heads in the actomyosin complex. Model calculations are presented which support this view. We argue that in a situation where an actomyosin complex is formed during contraction, one cannot describe the diffraction features as being either thick or thin filament based. Accordingly, the layer lines seen during tension generation are referred to as actomyosin layer lines. It is shown that these layer lines can be indexed as submultiples of a minimum axial repeat of approximately 218.7 nm. After lattice disorder effects are taken into account, the intensity increases on the 15th and 21st AM layer lines at spacings of approximately 14.58 and 10.4 nm respectively, show the same time course as tension rise. However, the time course of the intensity increase of the other actomyosin layer lines and of the spacing change (which is the same for both phenomena) shows a substantial lead over tension rise. These findings suggest that the actomyosin complex formed prior to tension rise is a non-tension-generating state and that this is followed by a transition of the complex to a tension-generating state. The intensity increase in the 15th actomyosin layer line, which parallels tension rise, can be accounted for assuming that in the tension-generating state the attached heads adopt (axially) a more perpendicular orientation with respect to the muscle axis than is seen at rest or in the non-tension-generating state. This suggests the existence of at least two structurally distinct interacting myosin head conformations.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative study of the supramolecular structure of frog sartorius and dorsal semitendinosus muscle.

This report describes a comparative X-ray diffraction study of the supramolecular structure of frog sartorius and semitendinosus muscles. For sarcomere lengths of 2.7 microns and below the X-ray diffraction diagrams of each muscle type are very similar; the only differences being that the diffraction diagram for semitendinosus muscles exhibit the presence of a broad diffraction band or a cluster of diffraction orders at a spacing of ca. 230.0 nm and, also, they lack a periodicity of ca. 102.0 nm. For sarcomere lengths greater than 2.7 microns disruption of the sarcomere from sartorius muscle occurs as seen by the loss of sampling in the diffraction diagram. The semitendinosus muscle can be stretched to much longer lengths (in excess of 3.0 microns) before a loss of sampling is detected. The data also shows that in the case of the semitendinosus muscle for long sarcomere lengths transverse bands of mass are able to move without retaining a defined distance to either the Z or the M lines. This is not observed in the case of the sartorius muscle. Thus, at resolutions between ca. 3.6 microns and 7.50 nm significant ultrastructural differences between these two muscles are apparent. The data suggest that the ability of these mass bands to move may be responsible for the differences in the development of passive tension exhibited by these two muscles.

Two-dimensional time resolved X-ray diffraction of muscle: recent results.

This report provides a preliminary sketch of the results obtained in a two-dimensional time resolved X-ray diffraction study of "live" frog sartorius muscles undergoing isometric tetani. These results demonstrate the recently developed capability to record time resolved (10 msec time resolution), two-dimensional X-ray diffraction diagrams throughout the cycle of contraction. The correlation between the time courses of the diffraction features in the whole of the diffraction diagram establishes a sequence of structural events, which suggest that during the transition from rest to the plateau of tension and the subsequent recovery, the following sequence of events takes place: a) Following the activation phase, which is best monitored by the increase of intensity on the second actin layer line at 18.0 nm spacing (5), there is the onset of three dimensional disorder due to the filaments losing their axial alignment and the myosin heads rotating azimuthally and moving radially outwards. A set of low-angle layer lines, following the actin based spacings seen in rigor (i.e., at spacings of ca. 36.5-37.5, 24.0 and 18.0 nm) become visible and those at ca. 24.0 and 18.0 nm appear to increase in intensity during this phase with a time course that cannot be determined accurately because of the proximity of the neighbouring first, second and third myosin layer lines and the weakness of these diffraction features. Whether the first of these layer lines increases or not is difficult to ascertain. Moreover, proper account of the loss in crystallinity during the development of tension must be made before the comparisons in intensity between the rest and peak of tension states have any significance. Nevertheless, these features together with the behaviour of the equatorial reflections and the meridional region of the third myosin layer line indicate that a sizeable fraction of the crossbridges may become axially disposed with an actin based periodicity. The formation of this complex does not immediately result in the generation of tension. The labelling of the thin filaments is also reflected in the main actin layer lines at 5.9 and 5.1 nm. b) The tension generating phase is monitored by the intensity changes in the meridional region of the third myosin layer line, which are best explained by a change in the orientation/conformation of the tension bearing crossbridges, (which probably adopt a more perpendicular orientation to the filament axis). c) At the end of stimulation, the crossbridges return to an axial spacing and axial orientation (although not yet azimuthal) similar to the one at rest.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium environment in encrusting deposits from urinary catheters investigated by interpretation of EXAFS spectra.

Extended x-ray absorption fine structure (EXAFS) spectra were recorded, above the K absorption edge of Ca, from 10 encrusted urinary (Foley) catheters obtained from 10 different patients. The presence of poorly crystalline apatite was demonstrated in all the deposits, even though this phase could not be detected in the x-ray powder diffraction patterns of most samples because of the obscuring effect of struvite, which was also present. Furthermore, the EXAFS spectra could be interpreted to yield quantitative information on the average short-range structure surrounding the Ca2+ ions in the poorly crystalline apatite.

Calcium environment in bone mineral determined by EXAFS spectroscopy.

Extended X-ray absorption fine structure (EXAFS) spectra were recorded, above the Ca K edge, from powdered mouse femurs. Spectra were interpreted on the basis of a model developed previously to explain the features of the EXAFS spectrum of fully crystalline hydroxyapatite. Eight shells of atoms surrounding Ca out 0.57 nm were required to explain the appearance of the EXAFS spectrum of bone. Shell radii and Debye-Waller factors were systematically varied to obtain the best fit between observed and theoretical spectra, calculated using exact spherical wave theory. The results were closely similar to those obtained previously from the interpretation of EXAFS spectra from poorly crystalline hydroxyapatite prepared by maturation of amorphous calcium phosphate. However, there appears to be slightly more disorder in bone mineral, perhaps as a result of its accommodating carbonate ions.

EXAFS study of structural disorder in carbonate-containing hydroxyapatites.

A structural characterization of pure hydroxyapatite and partially carbonated hydroxyapatites has been performed using EXAFS spectroscopy, X-ray diffraction, and infrared spectroscopy. Our findings show that marked structural changes within the hydroxyapatite unit cell accompany the substitution of the phosphate anion. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy has shown that the incorporation of carbonate into the phosphate site alters the structural geometry beyond the nearest neighbor oxygen coordination to calcium in a manner consistent with an increase in structural disorder. The nearest neighbor coordination to calcium is not detectably affected by the presence of carbonate.

Calcium phosphate in catheter encrustation.

Encrusted catheters from nine female patients were the source of samples of deposits which were examined by X-ray diffraction, atomic absorption spectroscopy, infra-red spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. In eight samples the only crystalline phase which could be clearly distinguished by X-ray diffraction was ammonium magnesium orthophosphate hexahydrate, NH4MgPO4 X 6H2O, which occurs naturally as the mineral struvite. However, atomic absorption spectroscopy revealed an appreciable concentration of calcium in all samples. Calcium phosphates have previously been detected in catheter deposits. Infra-red and EXAFS spectra were consistent with the calcium phosphate being present as a poorly crystalline hydroxyapatite. Thus the deposits appear to consist of a mixture of crystalline struvite and a form of hydroxyapatite which is not fully crystalline.

Atmospheric radiometry at submillimeter wavelengths.

The paper considers the application of broadband emission radiometry in the submillimeter (very far infrared) spectral region for studies of stratospheric water vapor. The detailed spectroscopy of the region is discussed and the effects of spectral contamination due to emission lines of other constituents, notably O(3) and O(2), and to a lesser extent N(2), are determined quantitatively. The O(3) lines arise through electric dipole transitions, the O(2) lines through magnetic dipole transitions, and the N(2) emission results from collision-induced electric dipole effects. Under certain circumstances, emission from these other species can represent a significant fraction of that due to H(2)O itself; it must either be corrected for rather carefully or eliminated in the design of the instrument.

Filter radiometer: the selective interferometer.

This paper describes a new type of filter radiometer-the Selective Interferometer Filter (SIF)-which has extremely high selectivity to the radiation from a given gas. The basic device is a double output Michelson interferometer, with mirrors fixed at zero geometrical path difference. It is shown that if a cell containing a gas is placed in each of the arms, the ensemble can be made to operate as a highly selective filter, passing radiation only very near the center frequencies corresponding to the absorption lines of this gas. This is a result of direct absorption effects and of the variation of refractive index with frequency and consequent modification of the optical path difference of the two arms of the interferometer. The device may, therefore, after calibration be operated as a highly selective ir radiometer; and a feature of importance in atmospheric and space applications is that it requires no internal moving parts to achieve this selectivity. Details of the device are presented, and a thorough examination of the practical realization of it is given.

Submillimeter-wave atmospheric and astrophysical spectroscopy.

The paper describes the results and methods of work which has been in progress during the past five years at the U.K. National Physical Laboratory and Queen Mary College, London on the submillimeter spectrum and its application to atmospheric and astrophysical problems. The paper begins with descriptions of the spectroscopic techniques evolved and used, which provide spectral resolution more than half an order of magnitude finer than previously available, particularly at the lower frequency end of the range, from 15 cm(-1) to 25 cm(-1). Excellent signal-to-noise ratios and reproducibility have been obtained and applied as shown in the second part of the paper to both atmospheric studies (chiefly at NPL) and astrophysical problems (chiefly at QMC). The former are illustrated with aircraft-borne measurements of minor species, such as H(2)O, O(3), HNO(3), and other gases, the latter with a consideration of the cosmic background at submillimeter wavelengths. A common thread is provided by developments in observational and interpretational spectroscopic techniques needed to overcome problems peculiar to this region of the spectrum. Our current progress in understanding the region and also prospects for future submillimeter spectroscopy are each brought into review in this work.