Laser-direct-write methods for fabrication of paper-based medical diagnostic sensors

We demonstrate the use of laser-based direct-write methods, namely laser-induced forward transfer and laser-induced photo-polymerization as printing and patterning tools for the fabrication of paper-based fluidic sensors that enable affordable point-of-care medical diagnostics

Gravitational Geons in 1+1 Dimensions

It is well known that general relativity does not admit gravitational geons that are stationary, asymptotically flat, singularity free and topologically trivial. However, it is likely that general relativity will receive corrections at large curvatures and the modified field equations may admit solutions corresponding to this type of geon. If geons are produced in the early universe and survive until today they could account for some of the dark matter that has been "observed" in galaxies and galactic clusters. In this paper I consider gravitational geons in 1+1 dimensional theories of gravity. I show that the Jackiw-Teitelboim theory with corrections proportional to $R^2$ and $\Box R$ admits gravitational geons. I also show that gravitational geons exist in a class of theories that includes Lagrangians proportional to $R^{2/3}$.Comment: 8 pages, a comment added, two references corrected, to appear in Classical and Quantum Gravit

Depth resolution of Piezoresponse force microscopy

Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection

Epitaxial lithium niobate thin films grown by chemical beam epitaxy on sapphire

Lithium Niobate (LiNbO3) is a versatile material with a number of remarkable qualities. It finds application in optical modulators because of its electro-optic properties. Nonlinearity opens its use in bio-physical applications where particles or wires of LiNbO3 can be used as highly localized optical probes. Optical frequency conversion is another possible use, as well. One of the current commercial applications of the material is in optical modulators in telecomunication devices. Nowadays bulk crystals of the material are used. However, in order to make devices more compact and affordable it is necessary to be able to produce LiNbO3 films on suitable substrates with sufficient crystalline and optical quality

Electro-optic coefficient enhancement in poled LiNbO₃ waveguides

Lithium niobate crystals (LN) show a significant electro-optic (EO) response which contributes to the fabrication of low-voltage operation, high speed integrated optical modulators routinely used in optical telecommunication and integrated optics [1]. A UV laser direct writing method for the fabrication of optical channel waveguides has been proposed and characterized recently [2-4]. Here we report on the enhancement of the electro-optic response of these UV laser-written LN waveguides as a result of a post-poling process. More specifically we have observed a 26% increase of the r33 coefficient compared to the bulk in LN waveguides, fabricated by direct UV writing, that have been subjected to poling inhibition [5]. Poling inhibition produces inverted ferroelectric domains which are only a few microns deep. These domains are formed exactly in the same place as the UV written tracks which are responsible for the waveguide formation, and they overlap significantly with the propagating waveguide mode as is illustrated schematically in Fig. 1. Due to the polarization-selective transmission in the UV-written waveguides only the r33 coefficient could be investigated. Fig. 1 Schematic of the cross section of a) a UV-written waveguide on a single domain substrate, and b) the tail-to-tail domain arrangement overlapping with the waveguide after poling-inhibition. Optical channel waveguides were fabricated by direct UV laser focused writing on the +z face of a z-cut undoped congruent LN substrate [4]. The sample was subsequently subjected to electric field poling using an externally applied electric field (~19.5 kV/mm) which resulted in local poling-inhibited domains of limited depth that overlap with the waveguides as shown in Fig. 1b [5,6]. The electro-optic response was evaluated interferometrically by placing the waveguides in one branch of a Mach-Zehnder interferometer [3]. A set of titanium in-diffused waveguides was used as a control sample to provide the background measurement of the bulk for the r33 coefficient. The measured values of the electro-optic coefficient (r33) in the poling-inhibited samples proved to be systematically higher than the value obtained with the control sample of unpoled titanium in-diffused waveguides which was 35 pm/V. The highest value of the r33 coefficient that was measured in the poling-inhibited waveguides was 44.2 pm/V, which corresponds to an enhancement of 26% as compared to the reference Ti indiffused waveguide sample. The observed enhancement in the value of the EO coefficient is attributed to the strain which is associated with the presence of a tail-to-tail domain boundary that surrounds the optical waveguide channel as illustrated in Fig. 1b. The enhancement of the EO coefficient varied for waveguides which were fabricated under different UV irradiation conditions. The irradiation conditions affect both the waveguide mode confinement and the depth of the poling-inhibited domains. This suggests that the enhancement can be further optimized and even applied to other waveguide systems such as titanium in-diffused and proton exchanged channel guides

Physicians' acquaintance with a new procedure results in higher patient referral: experience of Kosovo in coronary angiography

The first coronary angiography in Kosovo was completed in 2003. We analyzed coronary angiographies performed in our center from October 2003 until October 2009 divided into two 3-year periods. The aims of our study were: to compare the number of coronary angiographies completed in the two periods; to evaluate the prevalence of normal coronary angiographies diagnosed in the first period compared to the second period; and to assess the prevalence of advanced coronary artery disease in the first three years compared to the last three years. This was a prospective angiography study that included 1,139 patients. The first group had 422 patients, who underwent the angiography procedure during the first three years, and the second group had 717 patients that went through the procedure during the last three years. In the first year, 109 coronary angiographies were completed, followed by 137, 176, 213, 218 and 286 (P<0.001) procedures in the subsequent years. In the first period, a normal or near-normal coronary artery profile was found in 27% of patients, while this figure rose to approximately 39% in the second period (P=0.004). Advanced coronary artery disease was found in 45% of the patients who underwent coronary angiography during the first three years, whereas this figure was only 24% of cases during the second period (P<0.001). We believe that the availability of specialized resources and the physicians' familiarity with coronary angiography in our country influenced their decision to refer more patients for this procedure

Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-

We report the first observation of the baryonic flavor-changing neutral current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a statistical significance of 5.8 Gaussian standard deviations. This measurement uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV collected by the CDF II detector at the Tevatron collider. The total and differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}. We also report the first measurement of the differential branching ratio of B_s -> phi mu+ mu- using 49 signal events. In addition, we report branching ratios for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.Comment: 8 pages, 2 figures, 4 tables. Submitted to Phys. Rev. Let

Reflection second harmonic generation on a z-cut congruent lithium niobate crystal

Reflection second harmonic generation experiments were performed on z-cut congruent lithium niobate crystals (LiNbO3) to reveal the interfacial layer symmetry as the crystal is rotated around the z-axis. To suppress the bulk contribution, the fundamental wavelength was selected to be 532 nm resulting in second harmonic generation at a wavelength within the absorption region of the crystal. The polarity of the direction of the y-axis was determined from second harmonic generation data and used to show that this direction also inverts during domain inversion