Spectral Current Density and Responsivity Scaling for Fourier Transform Photocurrent Spectroscopy

We propose and experimentally verify two methods to scale arbitrary units to photocurrent spectral density (A/eV) in Fourier Transform Photocurrent (FTPC) spectroscopy. We also propose the FTPC scaling to responsivity (A/W), provided a narrow-band optical power measurement is available. The constant background of the interferogram provides a precise determination of the photocurrent spectral density. The second method relies on the scaled amplitude of the interferogram. Although the latter method leads to more significant errors, it still provides good order of magnitude estimates of the total photocurrent. We demonstrate the technique on a calibrated InGaAs diode and weak responsivity SiC interdigital sensors. We identify a series of impurity-band and interband transitions in the SiC sensors.Comment: 5 pages, 4 figure

Sub-surface alteration and related change in reflectance spectra of space-weathered materials

Context. Airless planetary bodies are studied mainly by remote sensing methods. Reflectance spectroscopy is often used to derive their compositions. One of the main complications for the interpretation of reflectance spectra is surface alteration by space weathering caused by irradiation by solar wind and micrometeoroid particles. Aims. We aim to evaluate the damage to the samples from H+ and laser irradiation and relate it to the observed alteration in the spectra. Methods. We used olivine (OL) and pyroxene (OPX) pellets irradiated by 5 keV H+ ions and individual femtosecond laser pulses and measured their visible (VIS) and near-infrared (NIR) spectra. We observed the pellets with scanning and transmission electron microscopy. We studied structural, mineralogical, and chemical modifications in the samples. Finally, we connected the material observations to changes in the reflectance spectra. Results. In both minerals, H+ irradiation induces partially amorphous sub-surface layers containing small vesicles. In OL pellets, these vesicles are more tightly packed than in OPX ones. Any related spectral change is mainly in the VIS spectral slope. Changes due to laser irradiation are mostly dependent on the material's melting temperature. Of all the samples, only the laser-irradiated OL contains nanophase Fe particles, which induce detectable spectral slope change throughout the measured spectral range. Our results suggest that spectral changes at VIS-NIR wavelengths are mainly dependent on the thickness of (partially) amorphous sub-surface layers. Furthermore, amorphisation smooths micro-roughness, increasing the contribution of volume scattering and absorption over surface scattering. Conclusions. Soon after exposure to the space environment, the appearance of partially amorphous sub-surface layers results in rapid changes in the VIS spectral slope. In later stages (onset of micrometeoroid bombardment), we expect an emergence of nanoparticles to also mildly affect the NIR spectral slope. An increase in the dimensions of amorphous layers and vesicles in the more space-weathered material will only cause band-depth variation and darkening.Peer reviewe

Alagille Syndrome Mimicking Biliary Atresia in Early Infancy.

Alagille syndrome may mimic biliary atresia in early infancy. Since mutations in JAG1 typical for Alagille syndrome type 1 have also been found in biliary atresia, we aimed to identify JAG1 mutations in newborns with proven biliary atresia (n = 72). Five biliary atresia patients with cholestasis, one additional characteristic feature of Alagille syndrome and ambiguous liver histology were single heterozygotes for nonsense or frameshift mutations in JAG1. No mutations were found in the remaining 67 patients. All "biliary atresia" carriers of JAG1 null mutations developed typical Alagille syndrome at the age of three years. Our data do not support association of biliary atresia with JAG1 mutations, at least in Czech patients. Rapid testing for JAG1 mutations could prevent misdiagnosis of Alagille syndrome in early infancy and improve their outcome

Comparison of space weathering spectral changes induced by solar wind and micrometeoroid impacts using ion- and femtosecond-laser-irradiated olivine and pyroxene

Context. Space weathering is a process that changes the surface of airless planetary bodies. Prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. These processes alter planetary reflectance spectra and often modify their compositional diagnostic features. Aims. In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes. Methods. We used olivine and pyroxene pellets as proxies for planetary materials. To simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 keV and fluences of up to 10(18) particles cm(-2). To simulate micrometeoroid bombardment we used individual femtosecond laser pulses. We analysed the corresponding evolution of different spectral parameters, which we determined by applying the Modified Gaussian Model, and we also conducted principal component analysis. Results. The original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. The spectral slope changes seen in olivine are consistent with observations of A-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) Vesta. We also observed some differences in the spectral effects induced by the two weathering agents. Ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. This is most likely due to the different penetration depths of ions and laser pulses. Our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface.Peer reviewe

Clinical features present in carriers of <i>JAG1</i> mutations at the time of hospitalization for neonatal cholestasis and at 3 years of age.

<p>* siblings;</p><p>ERCP, endoscopic retrograde cholangiopancreatography; BA, biliary atresia; BA type 3 –gallbladder, cystic duct and common bile duct are patent; BA type 4 –atresia of all the extrahepatic bile ducts; clinical features were present (+) or missing (-),</p><p>^# indicates clinical features not present at the age of 2 months;</p><p>AGS criteria indicate the number of major clinical features (diagnostic criteria) of Alagille syndrome present at the age of 2 months and 3 years, respectively.</p><p>Clinical features present in carriers of <i>JAG1</i> mutations at the time of hospitalization for neonatal cholestasis and at 3 years of age.</p

Schematic representation of the Jagged1 protein and spliced <i>JAG1</i> mRNA with mutations found in our patients.

<p>Schematic representation of the Jagged1 protein and spliced <i>JAG1</i> mRNA with mutations found in our patients.</p

Mutations in <i>JAG1</i> found in patients with biliary atresia and Alagille syndrome.

<p>* siblings;</p><p>AGS, Alagille syndrome; BA, biliary atresia; novel mutations are in <b>bold</b>.</p><p>Mutations in <i>JAG1</i> found in patients with biliary atresia and Alagille syndrome.</p