Quasar 3C 298: a test-case for meteoritic nanodiamond 3.5 µm emission

Aims. We calculate the dust emission expected at 3.43 and 3.53 µm if meteoritic (i.e. hydrogenated) nanodiamonds are responsible for most of the far-UV break observed in quasars. Methods. We integrate the UV flux that hydrogenated nanodiamonds must absorb to reproduce the far-UV break. Based on laboratory spectra of H-terminated diamond surfaces, we analyse the radiative energy budget and derive theoretically the IR emission profiles expected for possible C-H surface stretch modes of the diamonds. Results. Using as test case a spectrum of 3C 298 provided by the Spitzer Observatory, we do not find evidence of these emission bands. Conclusions. While diamonds without surface adsorbates remain a viable candidate for explaining the far-UV break observed in quasars, hydrogenated nanodiamonds appear to be ruled out, as they would give rise to IR emission bands, which have not been observed so far

Phytoplankton, bacterioplankton and nitrate reductase activity distribution in relation to physical structure in the northern Alborán Sea and Gulf of Cadiz (southern Iberian Peninsula)

The IctioAlborán-Cadiz 95 cruise (July 1995) covered the northwest sector of the Alborán Sea, the Straits of Gibraltar and the Gulf of Cadiz. We present and discuss the distribution of phytoand bacterioplankton abundance, nitrate concentration and nitrate reductase (NR) activity according to circulation patterns described previously in the literature. The water-column integrated values of chlorophyll-a in the Alborán Sea were higher and more variable (12 to 318 mg m⁻³) than in the Gulf of Cadiz (3 to 49 mg m⁻³). This reflects the higher dynamism of the Alborán sector, related to the existence of characteristic mesoscale physical structures. The plankton (2-80 μm equivalent spherical diameter) in the upwelling region of the Alborán Sea had a biovolume 30 times higher than in the nutrient-poorer water of the Gulf of Cadiz. Large organisms were abundant and dominated the size spectrum of one coastal station in the Alborán zone, whereas the slope of the size spectrum became more negative at the Gulf of Cadiz station, as a consequence of the dominance of small cells. Bacterial abundance maxima ( 3 X 10⁶ bact ml⁻¹) also occurred in the upwelling region. We found relatively high nitrate and chlorophyll a concentrations in Cape Trafalgar's cold surface waters, probably due to the interaction between topography and strong tidal currents. The spatial pattern of the NR activity is discussed according to chlorophyll a, nitrate and bacteria distributions. The existence of high NR activity but low chlorophyll a and bacterial abundance suggests that this could be related with dissimilatory activity in large-sized particles.La campaña IctioAlborán-Cádiz 95 (julio de 1995) cubrió el sector noroeste del mar de Alborán, estrecho de Gibraltar y golfo de Cádiz. En este trabajo se presentan y discuten las distribuciones de abundancia de fitoplancton y bacterioplancton, concentración de nitrato y actividad nitrato reductasa (NR) de acuerdo con los patrones de circulación descritos en la bibliografía. Los valores de clorofila a integrados en la columna de agua en Alborán fueron mayores y más variables (12 a 318 mg/m³) que en el golfo de Cádiz (3 a 49 mg/m³). Esto refleja el mayor dinamismo de la zona de Alborán, relacionado con la existencia de estructuras físicas características a mesoescala. El análisis de la comunidad nano-microplanctónica (2-80 μm, diametro esférico equivalente) de la región de afloramiento del mar de Alborán mostró un biovolumen 30 veces mayor que el de aguas más pobres en nutrientes del golfo de Cádiz. Por otro lado, el espectro de tamaños en una estación costera de Alborán está dominado por organismos planctónicos grandes, mientras que la pendiente del espectro de tamaño se hace más negativa en una estación del golfo de Cádiz, como consecuencia de la mayor abundancia de plancton de pequeño tamaño. En la región de afloramiento se dieron también máximos de abundancia bacteriana ( 3 X 10⁶ bact ml⁻¹). Se han encontrado valores relativamente altos de nitrato y clorofila a en las frías aguas superficiales cercanas al cabo de Trafalgar, lo que se debe, probablemente, a la interacción entre topografía y fuertes corrientes mareales. Se discute el patrón espacial de la actividad NR en relación con las distribuciones de clorofila a, nitrato y bacterias. En muestras con valores elevados de actividad NR pero bajos de clorofila y abundancia de bacterias, se sugiere que esta actividad se relaciona con actividad disimilatoria en agregados de gran tamaño.Instituto Español de Oceanografí

The emission line spectrum of the UV deficient quasar Ton 34: evidence of shock excitation?

Emission lines in quasars are believed to originate from a photoionized plasma. There are, however, some emission features which appear to be collisionally excited, such as the FeII multiplet bands. Shortward of Ly_alpha, there also are a few permitted lines of species from low to intermediate ionization. Ton 34 (z=1.928) exhibits the steepest far-UV continuum decline known (Fnu propto nu^{-5.3}) shortward of 1050A. This object also emits unusually strong low to intermediate excitation permitted lines shortward of the Lyman limit. Using archive spectra of Ton 34 from HST, IUE and Palomar, we measure the fluxes of all the lines present in the spectra and compare their relative intensities with those observed in composite quasar spectra. Our analysis reveals unusual strengths with respect to Ly_alpha of the following low to intermediate excitation permitted lines: OII+OIII (835A), NIII+OIII (686-703A) and NIII+NIV (765A). We compare the observed line spectrum with both photoionization and shock models. Photoionization cannot reproduce the strengths of these far-UV lines. Shocks with Vs ~ 100 km/s turn out to be extremely efficient emitters of these lines and are favored as excitation mechanism.Comment: 5 figures, accepted for publication in A&

Pore formation of phospholipid membranes by the action of two hemolytic arachnid peptides of different size

AbstractPin2 and Oxki1 are cationic amphipathic peptides that permeate lipid membranes through formation of pores. Their mechanism of binding to phosphocholine (PC) membranes differs. Spin-probe experiments showed that both Pin2 and Oxki1 penetrate the lipid membrane of small unilamellar vesicles (SUVs). Moreover, the leakage of calcein and dextrans from PC vesicles showed that Pin2 agrees with the accumulation of peptides on lipid membranes and form pores of different size. On the other hand, Oxki1 did not act strictly cooperatively and form pores of limited size

Real-time QFT Control for Temperature in Greenhouses

Sudden changes in a greenhouse environment negatively impact the development and production of crops, especially in greenhouses with natural ventilation when temperatures are low at night and change rapidly due to wet winds. To mitigate these variations, a design of a robust controller based on Quantitative Feedback Theory (QFT) as from a Smith predictor structure for the dead-time system is proposed. This structure offers high stability based on the gain margin, the phase margin, and the rejection of disturbances in the system output. This design was contrasted with a PID controller based on performance indices, according to the transient response and error in the presence of changes in the point of operation and charge disturbances. Final results showed that the dynamic response of the QFT controller improved compared to PID controller results