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In this work we theoretically investigate quantum confined Stark effect of intersubband transitions in asymmetric Ge/SiGe quantum wells for intensity modulation in the mid-infrared. Our calculations show that extinction ratios up to 1 dB and modulation speeds of several tens of GHz could be obtained in 100 µm long waveguides.
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Extending and controlling the spectral range of light detectors is very appealing for several sensing and imaging applications. Here we report on a normal incidence dual band photodetector operating in the visible and near infrared with a bias tunable spectral response. The device architecture is a germanium on silicon epitaxial structure made of two back-to-back connected photodiodes. The photodetectors show a broad photoresponse extending from 390nm to 1600nm with the capability to electronically select the shorter (400-1100 nm) or the longer (1000-1600 nm) portion with a relatively low applied voltage. Devices exhibit peak VIS and NIR responsivities of 0.33 and 0.63 A/W, respectively, a low optical crosstalk (<-30dB), a wide dynamic range (>120dB) and, thanks to their low voltage operation, maximum specific detectivities of 7·1011cmHz1/2/W and 2·1010cmHz1/2/W in the VIS and NIR, respectively.
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In this work we investigate the implementation of ultra-wideband polarization rotator in the mid-infrared spectral region. A new design method of the rotation section is proposed, yielding a polarization rotator with an extinction ratio of at least 15 dB in a wavelength range of 2 µm. For a spectral range wider than 3.8 µm, an extinction ratio of at least 10 dB is achieved for this design. The device is 1660 µm long and the associated insertion loss is below 1.2 dB on the full operational wavelength range. The influence of geometrical parameters with respect to the design method to obtain such a broadband behavior is discussed. Finally, to increase the tolerance to fabrication errors, a tapered rotator design is proposed. Such a device can support up to ± 100 nm fabrication errors and still guarantees remarkable broadband behavior. To the best of our knowledge, this is the first time an integrated polarization rotator is designed to operate for the wavelength range of 4 to 9 µm with a bandwidth exceeding 2 µm.
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Mid-infrared (mid-IR) silicon photonics is expected to lead key advances in different areas including spectroscopy, remote sensing, nonlinear optics or free-space communications, among others. Still, the inherent limitations of the silicon-on-insulator (SOI) technology, namely the early mid-IR absorption of silicon oxide and silicon at λ~3.6 µm and at λ ~8.5 µm respectively, remain the main stumbling blocks that prevent this platform to fully exploit the mid-IR spectrum (λ ~2-20 µm). Here, we propose using a compact Ge-rich graded-index Si1-xGex platform to overcome this constraint. A flat propagation loss characteristic as low as 2-3 dB/cm over a wavelength span from λ = 5.5 µm to 8.5 µm is demonstrated in Ge-rich Si1-xGex waveguides of only 6 µm thick. The comparison of three different waveguides design with different vertical index profiles demonstrates the benefit of reducing the fraction of the guided mode that overlaps with the Si substrate to obtain such flat low loss behavior. Such Ge-rich Si1-xGex platforms may open the route towards the implementation of mid-IR photonic integrated circuits with low-loss beyond the Si multi-phonon absorption band onset, hence truly exploiting the full Ge transparency window up to λ ~15 µm.
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This work explores the use of Ge-rich graded-index Si1-xGex rib waveguides as building blocks to develop integrated nonlinear optical devices for broadband operation in the mid-IR. The vertical Ge gradient concentration in the waveguide core renders unique properties to the guided optical mode, providing tight mode confinement over a broadband mid-IR wavelength range from λ = 3 µm to 8 µm. Additionally, the gradual vertical confinement pulls the optical mode upwards in the waveguide core, overlapping with the Ge-rich area where the nonlinear refractive index is larger. Moreover, the Ge-rich graded-index Si1-xGex waveguides allow efficient tailoring of the chromatic dispersion curves, achieving flat anomalous dispersion for the quasi-TM optical mode with D ≤ 14 ps/nm/km over a ~1.4 octave span while retaining an optimum third-order nonlinear parameter, γeff. These results confirm the potential of Ge-rich graded-index Si1-xGex waveguides as an attractive platform to develop mid-IR nonlinear approaches requiring broadband dispersion engineering.
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We exploit the spin-Hall effect to generate a uniform pure spin current in an epitaxial n-doped Ge channel, and we detect the electrically induced spin accumulation, transverse to the injected charge current density, with polar magneto-optical Kerr microscopy at a low temperature. We show that a large spin density up to 400 µm^{-3} can be achieved at the edges of the 100-µm-wide Ge channel for an applied electric field lower than 5 mV/µm. We find that the spin density linearly decreases toward the center of the Ge bar, due to the large spin diffusion length, and such a decay is much slower than the exponential one observed in III-V semiconductors, allowing very large spin accumulations over a length scale of tens of micrometers. This lays the foundation for multiterminal spintronic devices, where different spin voltages can be exploited as inputs for magnetologic gates on the same Ge platform.
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Ge on Si micro-disk, ring and racetrack cavities are fabricated and strained using silicon nitride stressor layers. Photoluminescence measurements demonstrate emission at wavelengths ≥ 2.3 µm, and the highest strained samples demonstrate in-plane, tensile strains of > 2 %, as measured by Raman spectroscopy. Strain analysis of the micro-disk structures demonstrate that shear strains are present in circular cavities, which can detrimentally effect the carrier concentration for direct band transitions. The advantages and disadvantages of each type of proposed cavity structure are discussed.
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The room temperature photoluminescence from Ge nanopillars has been extended from 1.6 µm to above 2.25 µm wavelength through the application of tensile stress from silicon nitride stressors deposited by inductively-coupled-plasma plasma-enhanced chemical-vapour-deposition. Photoluminescence measurements demonstrate biaxial equivalent tensile strains of up to â¼ 1.35% in square topped nanopillars with side lengths of 200 nm. Biaxial equivalent strains of 0.9% are observed in 300 nm square top pillars, confirmed by confocal Raman spectroscopy. Finite element modelling demonstrates that an all-around stressor layer is preferable to a top only stressor, as it increases the hydrostatic component of the strain, leading to an increased shift in the band-edge and improved uniformity over top-surface only stressors layers.
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Today, in many European countries, people are looking for wild edible plants to experience new tastes and flavors, by following the new trend of being green and environmentally friendly. Young borage and spinach leaves can be easily confused by inexpert pickers with those of other plants, including poisonous ones, such as Mandragora autumnalis Bertol. (mandrake) or Digitalis purpurea L. (foxglove), common in southern and northern Italy respectively. In the last twenty years, several cases of intoxication by accidental ingestion of mandrake and foxglove have been reported. The purpose of this work was to perform a pharmacognostic characterization of young leaves from borage, mandrake, foxglove and spinach, by micro-morphological, molecular and phytochemical techniques. The results showed that each of the three techniques investigated could be sufficient alone to provide useful information for the identification of poisonous species helping the medical staff to manage quickly the poisoned patients. However, the multi-disciplinary approach proposed could be very useful to asses the presence of poisonous plants in complex matrices, to build a database containing morphological, molecular and phytochemical data for the identification of poisonous species or in forensic toxicology, given their increasingly frequent use due to their low cost and relatively common availability.
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Folhas de Planta/química , Plantas Comestíveis/química , Plantas Tóxicas/química , Alcaloides/química , Cromatografia Gasosa , Glicosídeos Digitálicos/química , Cromatografia Gasosa-Espectrometria de Massas , Humanos , Itália , Região do Mediterrâneo , Compostos Fitoquímicos , Folhas de Planta/ultraestruturaRESUMO
The rat lithostathine gene was isolated from a genomic library using a rapid screening procedure involving PCR amplification. It was characterized over 2.7 kbp of gene sequence and 2.43 kbp of 5'-flanking sequence. The 5'-end of the coding sequence was determined by primer extension of lithostathine mRNA. The lithosathine sequence spanned over six exons. The promoter region of the gene contained the TATAAA and CCAAT consensus sequences 30 and 107 bp upstream of the cap site, respectively. Furthermore, a tract of (TG)22 repeat, with potential Z-DNA conformation, was found at position-1081.
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Proteínas de Ligação ao Cálcio/genética , Proteínas do Tecido Nervoso , Animais , Sequência de Bases , Proteínas de Ligação ao Cálcio/química , Clonagem Molecular , Litostatina , Conformação Molecular , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , RNA Mensageiro/análise , RatosRESUMO
During systematic analysis of the mRNAs expressed in a human colorectal carcinoma with the aim of evidencing new makers of the disease (Frigerio et al. (1995), in press), we isolated several clones corresponding to homologs of rat ribosomal protein mRNAs L5, L21, L27a, L28, S5, S9, S10 and S29. Because expression of several mRNAs encoding ribosomal proteins was found strongly altered during colorectal carcinogenesis, sequence of these transcripts, not previously described in human, was completed and their expression analyzed. Northern blot analysis of RNAs extracted from colorectal cancer and ajdacent normal tissue from 6 patients revealed in all of them perturbations of expression in cancer, compared to normal. No correlation could however be made between the level of expression and the severity of the disease. Yet, abnormal patterns with additional larger transcripts were observed in some patients for rpL5, rpL28 and rpS10.
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RNA Mensageiro/genética , Proteínas Ribossômicas/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Colo/metabolismo , Neoplasias Colorretais/genética , Primers do DNA , Humanos , Dados de Sequência Molecular , Ratos , Reto/metabolismo , Proteínas Ribossômicas/químicaRESUMO
A third member of the rat pancreatitis associated protein (PAP) gene family is described here. Its messenger RNA was cloned from an intestinal cDNA library and sequenced. The encoded protein, designated PAP III, shows 66% and 63% identity with the rat PAP I and II, respectively. The PAP III gene is constitutively expressed in the small intestine and in the pancreas with acute pancreatitis, but not in the healthy pancreas.
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Antígenos de Neoplasias , Biomarcadores Tumorais , Lectinas Tipo C , Pancreatite/genética , Proteínas/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , DNA Complementar/biossíntese , DNA Complementar/química , Intestino Delgado/metabolismo , Dados de Sequência Molecular , Pâncreas/metabolismo , Proteínas Associadas a Pancreatite , RNA Mensageiro/análise , RatosRESUMO
We have previously reported the coding sequence of the rat PAP II mRNA. We show in this paper the existence in rat pancreas of two forms of PAP II mRNA with identical coding sequence but a different 5'-untranslated region. We demonstrate that this is the result of a differential splicing.
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Antígenos de Neoplasias , Biomarcadores Tumorais , Lectinas Tipo C , Pâncreas/metabolismo , Proteínas/genética , RNA Mensageiro/análise , Animais , Sequência de Bases , Dados de Sequência Molecular , Proteínas Associadas a Pancreatite , Reação em Cadeia da Polimerase , Splicing de RNA , RatosRESUMO
The major isoenzyme of glutamine synthetase found in leaves of angiosperms is the chloroplastic form. However, pine seedlings contain two cytosolic glutamine synthetases in green cotyledons: GS1a, the predominant isoform, and GS1b, a minor enzyme whose relative amount is increased following phosphinotricin treatment. We have cloned a GS1b cDNA, and comparison with the previously reported GS1a cDNA sequence indicated that they correspond to separate cytosolic GS genes encoding distinct protein products. Phylogenetic analysis showed that the newly reported sequence is closer to cytosolic angiosperm GS than to GS1a, suggesting therefore that GS1a could be a divergent gymnospermous GS1 gene. Gene mapping using a F2 family of maritime pine showed co-localization of both GS genes on group 2 of the genetic linkage map. This result supports the proposed origin of different members of the GS1 family by adjacent gene duplication. The implications for gymnosperm genome organization are discussed.
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Citosol/enzimologia , Genoma de Planta , Glutamato-Amônia Ligase/genética , Isoenzimas/genética , Árvores/genética , Sequência de Bases , DNA Complementar , Dados de Sequência Molecular , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência do Ácido NucleicoRESUMO
Lithostathine is a pancreatic secretory protein which controls CaCO3 crystal growth in pancreatic juice. Trypsin hydrolysis of the molecule generates two fragments of 11 and 133 amino acids. The N-terminal undecapeptide bears the inhibitory activity for crystal growth. We demonstrate that the C-terminal part of the molecule, which is structurally related to Ca(2+)-dependent lectins, can induce bacterial aggregation. Ca(2+)- and pH-dependent aggregation was obtained for Escherichia coli strain KH 802 and 9 of 19 strains isolated from the predominant flora of human feces. Aggregation of E. coli could be reversed by dilution and bacteria could resume normal growth. Lithostathine is apparently the only component of normal pancreatic juice displaying such activity. Lithostathine is therefore a bifunctional protein which might be involved in the control of the bacterial ecosystem in the intestine.
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Carbonato de Cálcio/química , Proteínas de Ligação ao Cálcio/farmacologia , Escherichia coli/fisiologia , Proteínas do Tecido Nervoso , Suco Pancreático/química , Animais , Aderência Bacteriana/efeitos dos fármacos , Cálcio/farmacologia , Proteínas de Ligação ao Cálcio/isolamento & purificação , Cromatografia Líquida de Alta Pressão , Cristalização , Escherichia coli/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Hemaglutinação , Humanos , Concentração de Íons de Hidrogênio , Litostatina , Fosfoproteínas/farmacologia , Coelhos , Ratos , Tripsina/farmacologiaRESUMO
The diffuse reflectance spectra and the trichromatic coordinates of diffusing stratified paints are modeled. Each layer contains its own pigments, and their optical properties are first determined from experiments. The radiative transfer equation is then solved by the auxiliary function method for modeling the total light scattered by the stratified systems. The results are in good agreement with experimental spectra and validate the modeling. The calculations are then applied on the same stratified systems to study the influence of the observation angle in a bidirectional configuration and to study the influence of the thickness of the layers in a given configuration. In both cases, the reflectance spectra and the trichromatic coordinates are calculated and compared.
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Rat pancreatitis-associated protein (PAP) mRNA is barely detectable in normal pancreas and overexpressed during acute pancreatitis (Iovanna, J., Orelle, B., Keim, V., and Dagorn J.-C. (1991) J. Biol. Chem. 266, 24664-24669). RNA amplification by reverse-transcriptase-coupled polymerase chain reaction showed that PAP mRNA was constitutively expressed in duodenum, jejunum, and ileum, at similar levels as in pancreas during the acute phase of pancreatitis. A weak expression was also detected in several other tissues. The rat PAP gene was isolated from a genomic library and characterized over 3.2 kilobases of gene sequence and 1.2 kilobases of 5'-flanking sequence. The 5' end of the coding sequence was determined by primer extension of the PAP transcript. Several potential regulatory elements were identified in the promoter region, including a pancreas-specific consensus sequence, two Pan1 (pancreas-specific) transcription activators, two IL-6 response elements, and one glucocorticoid response element. The PAP coding sequence spanned over six exons. The first three exons encoded the 5'-untranslated region of the mRNA, the signal peptide, and 39 amino acids of the NH2-terminal end of the mature protein, respectively. The other three exons encoded a domain of the protein with significant homology to the carbohydrate-recognition domain of animal lectins. Sequence comparison of the PAP gene with 13 carbohydrate-recognition domain-containing genes revealed that they derived from the same ancestor gene. Position of introns within the carbohydrate-recognition domain were different, however, suggesting that PAP belongs to a new group of lectins. These results support the hypothesis that genes encoding PAP and other lectins evolved from a common ancestor gene by intron gain.
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Antígenos de Neoplasias , Evolução Biológica , Biomarcadores Tumorais , Expressão Gênica , Lectinas Tipo C , Lectinas/genética , Pancreatite/genética , Proteínas/genética , Ratos/genética , Doença Aguda , Sequência de Aminoácidos , Animais , Sequência de Bases , Éxons , Variação Genética , Íntrons , Dados de Sequência Molecular , Oligonucleotídeos Antissenso , Especificidade de Órgãos , Proteínas Associadas a Pancreatite , Reação em Cadeia da Polimerase , Regiões Promotoras Genéticas , Biossíntese de Proteínas , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Homologia de Sequência de Aminoácidos , Transcrição GênicaRESUMO
The pancreatitis-associated protein (PAP) is a lectin-related secretory protein present in small amounts in the rat pancreas and overexpressed during the acute phase of pancreatitis. On the other hand, PAP is constitutively expressed in the intestinal tract but not in other tissues. We cloned from a pancreatic cDNA library two overlapping cDNAs encoding a protein structurally related to PAP. This second PAP, which was called PAP II, was the same size as the original PAP (PAP I) and showed 74.3% amino acid homology. Studies on gene expression demonstrated that PAP II mRNA concentration increased within 6 h following induction of pancreatitis, reached maximal levels (> 200 times control values) at 24-48 h, and decreased thereafter, similar to PAP I. However, PAP II mRNA could not be detected in the intestinal tract or in other tissues. We also isolated a PAP II genomic DNA fragment which was characterized over 2.7 kb of gene sequence and 1.9 kb of 5' flanking sequence. The 5' end of the coding sequence was determined by primer extension of the PAP II mRNA. The PAP II coding sequence spanned six exons separated by five introns. Several potential regulatory elements were identified in the promoter region, including two glucocorticoid-response elements and one IL-6-response element. Antibodies raised to a synthetic peptide of PAP II detected a single band in Western blot analysis of the pancreatic secretory proteins from rats with pancreatitis, with a M(r) compatible with the theoretical M(r) of PAP II.(ABSTRACT TRUNCATED AT 250 WORDS)
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Antígenos de Neoplasias , Biomarcadores Tumorais , Regulação da Expressão Gênica , Genes/genética , Lectinas Tipo C , Pancreatite/genética , Proteínas/genética , RNA Mensageiro/genética , Doença Aguda , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Éxons/genética , Íntrons/genética , Dados de Sequência Molecular , Suco Pancreático/química , Proteínas Associadas a Pancreatite , Ratos , Homologia de Sequência de Aminoácidos , Transcrição GênicaRESUMO
It is shown that a multilayer with repeated symmetric unit structure is equivalent to a homogeneous and optically biaxial medium for obliquely incident light, the three principal axes being normal to the plane of incidence, normal to the film plane, and normal to the other two. Unit thickness dependence and incident angle dependence of the dielectric tensor and the effective thickness are calculated using exact formulas. It is found that, at small unit structure thickness, the equivalent medium is almost uniaxial, the optical axis being normal to the film, and the effective thickness is very close to the mechanical one. Absorbing films are also envisaged and the domain of validity (in terms of unit structure thickness) of the uniaxial equivalent medium is defined by numerical examples.
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Dielectric thin films often present microstructures that give rise to a variation of the refractive index with the distance from the substrate. We propose a method of analysis of ellipsometric data for homogeneous and slightly inhomogeneous films that are deposited on transparent substrates. Assuming a linear refractive-index gradient, we are able to determine not only the average index and the thickness but also the degree of inhomogeneity of the films by spectroscopic ellipsometry at variable angles of incidence. We apply this method to titanium dioxide films deposited on glass, which present different degrees of inhomogeneity depending on the preparation conditions.