Detection and measurement of middle-distillate fuel vapors by use of tunable diode lasers.

A sensor for the rapid (10-ms response time) measurement of vapors from the hydrocarbon-based fuels JP-8, DF-2, and gasoline is described. The sensor is based on a previously reported laser-mixing technique that uses two tunable diode lasers emitting in the near-infrared spectral region [Appl. Opt. 39, 5006 (2000)] to measure concentrations of gases that have unstructured absorption spectra. The fiber-mixed laser beam consists of two wavelengths: one that is absorbed by the fuel vapor and one that is not absorbed. Sinusoidally modulating the power of the two lasers at the same frequency but 180 degrees out of phase allows a sinusoidal signal to be generated at the detector (when the target gas is present in the line of sight). The signal amplitude, measured by use of standard phase-sensitive detection techniques, is proportional to the fuel-vapor concentration. Limits of detection at room temperature are reported for the vapors of the three fuels studied. Improvements to be incorporated into the next generation of the sensor are discussed.

Copepod development rates in relation to genome size and 18S rDNA copy number.

It is known that body sizes and temperature-independent developmental durations within two genera of calanoid Copepoda (Crustacea) are positively related to nuclear DNA contents of their somatic nuclei. Evidently because of the constraint of similar cell numbers among the species, (nucleotypic) effects of nucleus size on cell size and on cell-level processes are expressed at the whole-organism level. Here, we show that developmental durations of eight species of five genera are also negatively related to their greatly differing numbers of 18S rRNA genes per unit DNA. We propose that levels of rDNA iteration among copepods have been controlled by natural selection to regulate ribosome concentrations, therefore protein production and development rates, independently of the large variations in genome sizes, which are in turn adapted to regulating cell and therefore body sizes.

High-sensitivity laser absorption measurements of broadband absorbers in the near-infrared spectral region.

We describe the development and characterization of a near-infrared diode-laser-based sensor to measure the vapor from trace gases having unstructured absorption spectra. The technique uses two equal amplitude-modulated laser beams, with the modulation of the two lasers differing in phase by 180 deg. One of the laser beams is at a wavelength absorbed by the gas [for these experiments, vapor is from pyridine (C(5)H(5)N)], and the second laser beam is at a wavelength at which no absorption occurs. The two laser beams are launched onto near-coincident paths by graded-index lens-tipped optical fibers. The mixed laser beam signal is detected by use of a single photodiode and is demodulated with standard phase-sensitive detection. Data are presented for the detection and measurement of vapor from pyridine (C(5)H(5)N) by use of the mixed laser technique. The discussion focuses on experimental determination of whether a compound exhibits unstructured absorption spectra (referred to here as a broadband absorber) and methods used to maximize sensitivity.

Unusually high numbers of ribosomal RNA genes in copepods (Arthropoda: Crustacea) and their relationship to genome size.

We report on copy numbers of 18S ribosomal RNA genes in three species of copepods (Crustacea: Copepoda), two of which possess an unusual arrangement in which 5S genes are included within the 18S-5.8S-28S repeat unit. Slot blots of genomic and standard DNA were hybridized with an 18S rRNA gene probe constructed from one of the marine species and hybridization was quantified using chemiluminescence. Diploid 18S rRNA gene copy numbers are estimated as ca. 15 300 and 33 500 in the marine species Calanus finmarchicus (13.0 pg DNA in 2C adult nuclei) and C. glacialis (24.2 pg DNA), respectively, and ca. 840 and 730 in two freshwater populations of Mesocyclops edax (both ca. 3 pg DNA) from Virginia and Nova Scotia, respectively. The roughly proportional relationship between 2C somatic nuclear DNA contents and rRNA gene copy number in the sibling species C. finmarchicus and C. glacialis may reflect polytenic replication of entire genomes during abrupt speciation events. Copy numbers may also reflect differential losses during embryonic chromatin diminution.

Growth in pinnipeds.

This review presents summary figures of, and fits growth curves to, data on body lengths (as standard length, SL, whenever possible) of pinnipeds at ages estimated to O.I y. (1) Generalized von Bertalanffy (vB) growth curves are fitted to most data: Lx = L infinity (I - ea(x-x0)b, Lx is length at age x, x0 is the origin of the curve (here chosen a priori as time of initiation of embryonic growth), L infinity is asymptotic length, a (which is negative) determines rate of approach to the asymptote, and b influences the 'shape' of the approach. (2) No single monotonic growth equation suffices for growth in length, which is linear before birth and remains so during early life. The vB equation is only suitable to describe mean lengths of newborns, and animals one or more years old. (3) Also, for males of polygynous species, two functions are needed to account for accelerated growth at puberty. Generally a Gompertz equation is adequate for adult males of these species. (4) The fitted growth equations permit statistical comparisons of sizes and growth rates, as well as of individual variability (as growth-curve residuals), among populations and species. (5) For the following species (including different populations when available), the reliability of data is assessed and parameters of growth curves are presented (with sexes separated where significantly different): walrus, California and Steller sea lions, Antarctic, subantarctic and northern fur seals, Hawaiian monk seal, crabeater, Weddell and Leopard seals, southern and northern elephant seals, bearded, hooded, ringed, Baikal, Caspian, spotted, harbour, harp, ribbon and grey seals. (6) Some novel findings pertain to individual species as follows. Although the Pacific walrus is generally stated to be the larger subspecies, females from Hudson Bay and males from Foxe Basin, in the eastern Canadian Arctic, may be as long as those from the Bering Sea. Although female Weddell seals have been assumed to grow larger than males, there is no significant difference in growth curves fitted to the most complete data. Uniquely among populations examined, the relative variability (absolute growth curve residuals/predicted lengths) of male southern elephant seals is amplified with age. Among ringed seals from Svalbard, the eastern, western and high Canadian Arctic, and the Bering, Chukchi, Okhotsk, Barents and Baltic Seas, asymptotic sizes are larger among those that breed on land-fast ice rather than floes, and size may be more variable in more extreme Arctic environments. The Baikal seal is confirmed as the smallest species of pinniped.(ABSTRACT TRUNCATED AT 400 WORDS)

Variable arrangement of 5S ribosomal genes within the ribosomal DNA repeats of arthropods.

The polymerase chain reaction and hybridization to genomic blots were used to investigate whether the previously observed inclusion of 5S ribosomal RNA genes in the 28S-18S ribosomal DNA intergenic regions of some crustacean species (copepods) could also be detected in other arthropods. Such an arrangement was found not only in other calanoid copepod species but also in a cirriped, an euphausid, and a spider. It is interesting that species from two different calanoid copepod genera do not have this type of arrangement. We conclude that the inclusion of 5S ribosomal RNA genes within the ribosomal DNA repeats has probably occurred repeatedly during the evolution of arthropod species and that the mechanism(s) responsible for these insertions could also be responsible for their loss.

Unusual variations in nuclear DNA contents in the marine copepod Pseudocalanus.

Variations in DNA/nucleus within adult females are similar, when normalized for mean differences, in the copepods Pseudocalanus sp. and Eurytemora herdmani. However, Pseudocalanus shows great variation among individuals, with no evidence of significant groupings (species?), except perhaps for a few individuals with abnormally small DNA values. Body lengths of adult female Pseudocalanus are approximately proportional to the cube root of DNA/nucleus. It is inferred that nuclear size, not nuclear number, determines body size, and this is supported by generally similar nuclear counts in newly hatched nauplii and among first copepodid stages. Although body size and development rate of Pseudocalanus had earlier been shown to be strongly heritable, an offspring-parent regression reflected no heritability of DNA/nucleus (and some abnormally small offspring values) under the probably suboptimal conditions of rearing. Some variability in DNA content of adult somatic nuclei may be related to chromatin diminution during embryogenesis. An unusual loss of nonchromosomal, Feulgen-positive material is documented for first cleavage in Pseudocalanus, but not E. herdmani.

Polyteny: A Source of Cryptic Speciation among Copepods.

A large form of the copepod Pseudocalanus is found in two warm, semi-landlocked fiords in arctic Canada, together with a similar but smaller form attributable to the widespread P. minutus. The large form has the same chromosomne number as P. minutus, but has larger chromosomes and a higher nuclear DNA content. There are suggestions in the literature that other similar polytenic and cryptic species occur among copepods.