Brillouin scattering for refractive index sensing in non-adiabatic tapers.

We demonstrate the use of non-adiabatic tapers for refractive index sensing in optical fibers based on Brillouin scattering. By exciting higher order optical modes along the taper, the Brillouin gain spectrum becomes multipeaked, where each peak exhibits a different sensitivity to the refractive index of the surrounding medium. By this method, we demonstrate a sensitivity enhancement of the Brillouin frequency shift to refractive index changes by a factor of ≈ 4, compared to an adiabatic taper with the same waist diameter. Furthermore, the use of the spectral difference between two Brillouin gain peaks provides a temperature-independent measurement of the external refractive index.

Hybrid Brillouin/Rayleigh sensor for multiparameter measurements in optical fibers.

We present a hybrid Brillouin/Rayleigh sensor for multiparameter sensing in optical fibers. The system makes use of a single laser pulse to excite both Rayleigh and Brillouin backscattering in the same optical fiber. In the detection path, the backscattered signals are separated based on their different wavelengths. The system is capable of determining simultaneously the Brillouin frequency shift (BFS) of the fiber, as well as the frequency contents of any vibration acting on the same fiber as recovered by phase sensitive OTDR (ϕ-OTDR) measurements. The reported experiments show the possibility to perform simultaneous temperature and vibration measurements, as well as to perform dynamic strain measurements combining the information provided by slope-assisted Brillouin scattering measurements, with those provided by amplitude-based ϕ-OTDR measurements.

Theoretical and experimental comparison of a distributed acoustic sensor at 850- and 1550-nm wavelengths.

In this paper, we analyze the performance of a distributed acoustic sensor at two different interrogation wavelengths. We show theoretically that, in a coherent optical time-domain reflectometry (OTDR) operating at 850 nm, the dynamic signal-to-noise ratio (SNR) is enhanced, compared to an identical configuration operating at 1550 nm. Such enhancement is maximum at the interrogating pulse input section, while decreasing along the fiber in virtue of the higher loss. Experimental tests, carried out using two heterodyne C-OTDR detection schemes operating at the analyzed wavelengths, confirm the SNR improvement.

Development and characterization of an integrated silicon micro flow cytometer.

This paper describes an innovative integrated micro flow cytometer that presents a new arrangement for the excitation/detection system. The sample liquid, containing the fluorescent marked particles/cells under analysis, is hydrodynamically squeezed into a narrow stream by two sheath flows so that the particles/cells flow individually through a detection region. The detection of the particles/cells emitted fluorescence is carried out by using a collection fiber placed orthogonally to the flow. The device is based on silicon hollow core antiresonant reflecting optical waveguides (ARROWs). ARROW geometry allows one to use the same channel to guide both the sample stream and the fluorescence excitation light, leading to a simplification of the optical configuration and to an increase of the signal-to-noise ratio. The integrated micro flow cytometer has been characterized by using biological samples marked with standard fluorochromes. The experimental investigation confirms the success of the proposed microdevice in the detection of cells.

Stimulated Brillouin scattering frequency-domain analysis in a single-mode optical fiber for distributed sensing.

A numerical and experimental analysis of the stimulated Brillouin scattering in a single-mode optical fiber for distributed sensing applications is carried out in the frequency domain. The theoretical model describing the Brillouin interaction is solved by taking into account the temporal dynamics of the acoustic wave that is involved. The simulations and the experimental results reveal the role played by the ac component of the acoustic wave, which is responsible for significant changes of the small-signal stimulated Brillouin scattering transfer function that occur when the modulation frequency rises above the natural Brillouin gain spectrum linewidth. One should take these effects into account to perform accurate signal processing of frequency-domain signals in high-resolution distributed sensing applications.

Frequency-domain approach to distributed fiber-optic Brillouin sensing.

A novel approach to distributed fiber-optic Brillouin sensing is presented and numerically analyzed. An integral equation that directly relates the Brillouin gain to the Brillouin signal is derived in the frequency domain, and from this result a new technique for the quantitative reconstruction of temperature-strain profiles along an optical fiber is developed. We achieve the reconstruction by minimizing a cost function that represents the error between the measured and the model data. We effectively perform such a minimization by representing the unknown (temperature-strain) profile with a finite number of parameters. Numerical results confirm the effectiveness of the proposed approach and its stability against noise in the data.

A novel chordin-like protein inhibitor for bone morphogenetic proteins expressed preferentially in mesenchymal cell lineages.

Chordin is a bone morphogenetic protein (BMP) inhibitor that has been identified as a factor dorsalizing the Xenopus embryo. A novel secreted protein, CHL (for chordin-like), with significant homology to chordin, was isolated from mouse bone marrow stromal cells. Injection of CHL RNA into Xenopus embryos induced a secondary axis. Recombinant CHL protein inhibited the BMP4-dependent differentiation of embryonic stem cells in vitro and interacted directly with BMPs, similar to chordin. However, CHL also weakly bound to TGFbetas. In situ hybridization revealed that the mouse CHL gene, located on the X chromosome, was expressed predominantly in mesenchyme-derived cell types: (1) the dermatome and limb bud mesenchyme and, later, the subdermal mesenchyme and the chondrocytes of the developing skeleton during embryogenesis and (2) a layer of fibroblasts/connective tissue cells in the gastrointestinal tract, the thick straight segments of kidney tubules, and the marrow stromal cells in adults. An exception was expression in the neural cells of the olfactory bulb and cerebellum. Interestingly, the spatiotemporal expression patterns of CHL were distinct from those of chordin in many areas examined. Thus, CHL may serve as an important BMP regulator for differentiating mesenchymal cells, especially during skeletogenesis, and for developing specific neurons.

Glutamatergic control of food intake in pigeons: effects of central injections of glutamate, NMDA, and AMPA receptor agonists and antagonists.

The possible involvement of glutamatergic mechanisms in the control of food intake was studied in free-feeding and in 24-h food-deprived (FD24) pigeons for 1 h after intracerebroventricular (i.c.v.) treatment with glutamate (Glu, 0, 50, 150, 300, and 600 nmol). Glu injections dose dependently induced decreases (30-65%) in food intake (FI) and feeding duration (FD), and increases in latency to start feeding (LSF) in FD24 animals, but not in free-feeding ones. None of these treatments affected noningestive behaviors (locomotion, sleep, and preening). In FD24 pigeons, i.c.v. treatments with N-methyl-D-aspartic acid (NMDA, 0.1, 1, 4, 8, or 16 nmol) or D,L-alpha-amino-3-hydroxy-isoxazole proprionic acid (AMPA, 0.1, 1, 4, or 8 nmol) decreased FI and FD, but left LSF unchanged compared to vehicle-treated FD24 controls. Kainic acid (0.1, 0.5, and 1 nmol), or [trans-(1S,3R)-ACPD-(5NH4OH)] (ACPD, 0.1, 1, 4, 8, and 16 nmol) left unchanged the ingestive profile of FD24 pigeons. Pretreatment with the NMDA receptor antagonist MK-801 (15 nmol) and the AMPA-kainate receptor antagonist CNQX (390 nmol), 20 min before an i.c.v. injection of Glu (300 nmol) induced a partial blockade of the Glu-induced decreases in FI and FD and completely inhibited the Glu-induced increase in LSF in FD24 pigeons. I.c.v. injections of MK-801 (30 nmol) and of CNQX (780 nmol) increased FI and FD and reduced LSF in free-feeding pigeons. A lower dose of MK-801 (15 nmol) increased FI and FD, but not LSF. Conversely, a lower dose of CNQX (390 nmol) reduced LSF without changing FI or FD. These findings indicate the involvement of Glu as a chemical mediator in the regulation of food intake in the pigeon, possibly acting on multiple central mechanisms in this species through NMDA- and AMPA-sensitive Glu receptors.

Disulfide assignment of the C-terminal cysteine knot of agouti-related protein (AGRP) by direct sequencing analysis.

We have assigned the disulfide structure of Md-65 agouti-related protein (Md65-AGRP) using differential reduction and alkylation followed by direct sequencing analysis. The mature human AGRP is a single polypeptide chain of 112 amino acid residues, consisting of an N-terminal acidic region and a unique C-terminal cysteine-rich domain. The C-terminal domain, a 48 amino acid peptide named Md65-AGRP, was expressed in Escherichia coil cells and refolded under different conditions from the mature recombinant protein. The disulfide bonds in the cystine knot structure of Md65-AGRP were partially reduced using tris(2-carboxyethyl) phosphine (TCEP) under acidic conditions, followed by alkylation with N-ethylmaleimide (NEM). The procedure generated several isoforms with varying degrees of NEM alkylation. The multiple forms of Md65-AGRP generated by partial reduction and NEM modification were then completely reduced and carboxymethylated to identify unreactive disulfide bonds. Differentially labeled Md65-AGRP were directly sequenced and analyzed by MALDI mass spectrometry. The results confirmed that Md65-AGRP contained the same disulfide structure as that of Md5-AGRP reported previously [Bures, E. J., Hui, J. O., Young, Y. et al. (1998) Biochemistry 37, 12172-12177].

Utilization of percutaneous transluminal coronary angioplasty for quality assurance in health care from 1983 to 1996.

OBJECTIVES: To examine the distribution of interventional cardiac catheterization laboratories, their case load, the time trends, and the regional variation of percutaneous transluminal cutaneous angioplasty (PTCA) utilization in Italy. METHODS: Analysis of data was provided by the annual reports of the Italian Group of Studies and Interventional Cardiology over the period from 1983 to 1996. RESULTS: The number of PTCA facilities and their use steadily increased, mainly in the North. In 1996 the utilization rate was 34 per 100,000 population, but only 60% of labs performed 200 or more procedures. CONCLUSIONS: Dramatic time trends and regional variations often took place without an epidemiology and technology assessment-based planning process.

Biochemical, biophysical, and pharmacological characterization of bacterially expressed human agouti-related protein.

The agouti-related protein gene (Agrp) is a novel gene implicated in the control of feeding behavior. The hypothalamic expression of Agrp is regulated by leptin, and overexpression of Agrp in transgenic animals results in obesity and diabetes. By analogy with the known actions of agouti, these data suggest a role for the Agrp gene product in the regulation of melanocortin receptors expressed in the central nervous system. The availability of recombinant, highly purified protein is required to fully address this potential interaction. A nearly full-length form of AGRP (MKd5-AGRP) was expressed in the cytosolic or soluble fraction of Escherichia coli and appeared as large intermolecular disulfide-bonded aggregates. Following oxidation, refolding, and purification, this protein was soluble, and eluted as a single symmetric peak on RP-HPLC. Circular dichroism studies indicated that the purified protein contains primarily random coil and beta-sheet secondary structure. Sedimentation velocity studies at neutral pH demonstrated that MKd5-AGRP is monomeric at low micromolar concentrations. Mobility shifts observed using SDS-PAGE under reducing and nonreducing conditions for bacterially expressed and mammalian expressed AGRP were identical, an indication of a similar disulfide structure. The purification to homogeneity of a second, truncated form of AGRP (Md65-AGRP) which was expressed in the insoluble or inclusion body fraction is also described. Both forms act as competitive antagonists of alpha-melanocyte stimulating hormone (alpha-MSH) at melanocortin-3 (MC-3) and melanocortin-4 receptors (MC-4). The demonstration that AGRP is an endogenous antagonist with respect to these receptors is a unique mechanism within the central nervous system, and has important implications in the control of feeding.

Food intake after adrenaline and noradrenaline injections into the hypothalamic paraventricular nucleus in pigeons.

The effects of local injections of adrenaline (Adr, 6 nmol) or noradrenaline (Nor, 16 nmol) into the paraventricular nucleus (PVN) and into other anterior hypothalamic districts on feeding behavior were examined in satiated pigeons bearing a chronically implanted cannula. When infused into the PVN, both Adr and Nor reliably elicited feeding responses during the first hour after the injection. Feeding responses to Adr injections were significantly higher than those evoked by Nor. Other behavioral measurements (sleep, exploratory, and preening) were not affected by these treatments. Local pretreatment with phentolamine (20 nmol) but not with propranolol (20 nmol) abolished the feeding response induced by both Adr and Nor into the PVN. Lateral hypothalamic sites were also shown to respond to catecholamine injections with an increase in feeding, followed also by an increased sleep-like behavior duration. Together with other evidence, the present results indicate that adrenergically mediated circuits into the avian PVN play an important role in the mechanisms of food intake control, equivalent to that observed in mammalian species.

Determination of disulfide structure in agouti-related protein (AGRP) by stepwise reduction and alkylation.

The agouti-related protein gene (Agrp) plays an important role in body weight regulation. The mature human protein is a single polypeptide chain of 112 amino acid residues, consisting of an N-terminal acidic region and a unique C-terminal cysteine-rich domain. The disulfide structure of recombinant human AGRP was determined by chemical methods using partial reduction with tris(2-carboxyethyl)phosphine under acidic conditions, followed by direct alkylation with N-ethylmaleimide or fluorescein-5-maleimide. Partial reduction and alkylation provided several forms of AGRP that were modified in a stepwise fashion. The resulting proteins were characterized by peptide mapping, sequence analysis, and mass spectrometry, showing that AGRP contained a highly reducible disulfide bond, C85-C109, followed by less reactive ones, C90-C97, C74-C88, C67-C82, and C81-C99, respectively. The chemically defined disulfide connectivity of the recombinant human AGRP was homologous to that of omega-agatoxin IVB except for an additional disulfide bond, C85-C109.

Real-time measurement of transverse-mode-mixing effects in a Q-switched Nd:YAG laser.

We describe a novel apparatus for the real-time characterization of transverse-mode-mixing effects by monitoring the fluctuations of the M(2) factor defined by Siegman [Proc. Soc. Photo-Opt. Instrum. Eng. 1224, 2 (1990)]. A comparison between the results provided by our approach and those obtained by the use of a standard measurement apparatus has shown a satisfactory agreement within the experimental uncertainty.

Purification and identification of brain-derived neurotrophic factor from human serum.

Brain-derived neurotrophic factor (BDNF), a 27-kDa noncovalently linked homodimer with subunits of approximately 13.5 kDa as viewed by SDS-PAGE, is thought to be primarily produced in the central nervous system. We report here the isolation of BDNF from pooled normal human sera, using a two-step purification process followed by SDS-PAGE, transfer to a polyvinylidene difluoride membrane, and subsequent identification of the protein by sequence analysis of the appropriate band(s) from the membrane. The level of BDNF in pooled human sera was estimated to be approximately 15 ng/ml as determined by an enzyme-linked immunosorbant assay. The average for six individuals was 18.9 +/- 5.7 ng/ml. There is an approximately 200-fold increase in the levels of BDNF in serum relative to plasma. Results from experiments using differential centrifugation suggest that the source of this increase is due to release from platelets. The presence of high levels of BDNF in serum suggests a role for this neurotrophin either in nerve repair at sites of injured tissue or in nonneuronal functions.

Transverse mode analysis of a laser beam by near- and far-field intensity measurements.

A quantitative measurement of laser-beam quality can be performed by determination of the presence of multiple transverse modes of the laser oscillator and by calculation of their power content. Along this line of argument, we discuss a new approach that, starting from near-field and far-field intensity measurements, can evaluate the complex excitation coefficients of the transverse modes in a laser beam. The exploitation of near-field measurements sharply improves the performances of the technique in those cases in which only far-field measurements are used. The validity of the method is confirmed by several accurate numerical simulations and by some experimental results relative to a multimode Q-switched Nd:YAG laser.

[Multidimensional diagnosis in general medicine. Comparative study of the use of various instruments]. / La diagnosi multidimensionale in medicina generale. Studio comparativo sull'uso di alcuni strumenti.

This study was performed to test three instruments for functional status assessment in General Practice: the Dartmouth Coop Charts (COOP Charts), the Functional Status Questionnaire (FSQ) and the Duke University Health Profile (DUHP). All the instruments covered a score of functional aspects in physical, mental and social areas, providing a multidimensional measure of health status. We used these three instruments, validated by international studies, to acquire information concerning their feasibility and acceptability among patients from rural communities needing primary care and to test their validity in differentiating between patient subgroups. The COOP Charts, the FSQ and the DUHP were administered by physicians respectively to 98, 100 and 97 patients, waiting for a visit in the ambulatories of their General Practitioner. Answers relating to each instrument were analyzed according to sex, age and education of patients. All the instruments seemed to be feasible and acceptable, but only the COOP Charts and the FSQ were able to discriminate between different sex, age and scolarity groups. Taking into account the need to elaborate answers according to a formula when using the FSQ, we concluded that the best instrument for General Practice to provide a multidimensional measure of health status seems to be the COOP Charts.

Properties of variant forms of human stem cell factor recombinantly expressed in Escherichia coli.

The gene for human stem cell factor (SCF) encodes a leader sequence followed by 248 amino acids (Martin et al., 1990, Cell 63, 203). Of these 248 amino acids, the first 189 correspond to an extracellular domain and the remainder correspond to a hydrophobic transmembrane domain plus a cytoplasmic domain. A naturally occurring soluble form, released by proteolytic cleavage after amino acid 165, has been described. An alternatively spliced mRNA, lacking the codons for exon 6, has also been described. Since the amino acids encoded by exon 6 include the proteolytic cleavage site, the form expressed from the alternatively spliced mRNA tends to remain membrane-bound. In the present study, we have begun to explore structure/function relationships within the extracellular domain of SCF. Forms beginning at amino acid 1 (after the leader sequence) and ranging from 127 to 189 at the C-terminus have been recombinantly expressed in Escherichia coli and purified. In addition, forms missing the amino acids encoded by exon 6, forms missing up to 10 amino acids from the N-terminus, and forms with disulfide bond alterations have been expressed and purified. The forms have been characterized structurally, as well as functionally, in quantitative cell proliferation and receptor-binding assays. The results indicate that amino acids 1-141 comprise a structural and functional core and allow conclusions about the necessity of each of the two disulfide bonds for structure and function.

Characterization of the transverse modes in a laser beam: analysis and application to a Q-switched Nd:YAG laser.

We have developed a numerical code that, starting from far-field intensity measurements, is able to evaluate the excitation coefficients of the transverse modes in a laser system.Both the coherent and incoherent mode cases are addressed, and, while the incoherent case is shown to be equivalent to a linear problem, the coherent case is discussed through its equivalence to the phase-retrieval problem. Problems arising from both ill posedness and the nonlinearity are discussed in detail.The validity of our approach is confirmed by several numerical simulations and some experimental results on the characterization of a Q-switched Nd:YAG laser.