Silicon nanoparticles as Raman scattering enhancers.

In this communication we demonstrate the large amplification values of the Raman signal of organic molecules attached to silicon nanoparticles (SiNPs). Light induced Mie resonances of high refractive index particles generate strong evanescent electromagnetic (EM) fields, thus boosting the Raman signal of species attached to the nanoparticles. The interest of this process is justified by the wide range of experimental configurations that can be implemented including photonic crystals, the sharp spectral resonances easily tuneable with the particle size, the biocompatibility and biodegradability of silicon, and the possibility of direct analysis of molecules that do not contain functional groups with high affinity for gold and silver. Additionally, silicon nanoparticles present stronger field enhancement due to Mie resonances at larger sizes than gold.

All-silicon spherical-Mie-resonator photodiode with spectral response in the infrared region.

Silicon is the material of choice for visible light photodetection and solar cell fabrication. However, due to the intrinsic band gap properties of silicon, most infrared photons are energetically useless. Here, we show the first example of a photodiode developed on a micrometre scale sphere made of polycrystalline silicon whose photocurrent shows the Mie modes of a classical spherical resonator. The long dwell time of resonating photons enhances the photocurrent response, extending it into the infrared region well beyond the absorption edge of bulk silicon. It opens the door for developing solar cells and photodetectors that may harvest infrared light more efficiently than silicon photovoltaic devices that are so far developed.

Looking through the mirror: optical microcavity-mirror image photonic interaction.

Although science fiction literature and art portray extraordinary stories of people interacting with their images behind a mirror, we know that they are not real and belong to the realm of fantasy. However, it is well known that charges or magnets near a good electrical conductor experience real attractive or repulsive forces, respectively, originating in the interaction with their images. Here, we show strong interaction between an optical microcavity and its image under external illumination. Specifically, we use silicon nanospheres whose high refractive index makes well-defined optical resonances feasible. The strong interaction produces attractive and repulsive forces depending on incident wavelength, cavity-metal separation and resonance mode symmetry. These intense repulsive photonic forces warrant a new kind of optical levitation that allows us to accurately manipulate small particles, with important consequences for microscopy, optical sensing and control of light by light at the nanoscale.

All silicon waveguide spherical microcavity coupler device.

A coupler based on silicon spherical microcavities coupled to silicon waveguides for telecom wavelengths is presented. The light scattered by the microcavity is detected and analyzed as a function of the wavelength. The transmittance signal through the waveguide is strongly attenuated (up to 25 dB) at wavelengths corresponding to the Mie resonances of the microcavity. The coupling between the microcavity and the waveguide is experimentally demonstrated and theoretically modeled with the help of FDTD calculations.

Low order modes in microcavities based on silicon colloids.

Silicon colloids based microcavities, with sphere size between 1 and 3 micrometers, have been synthesized and optically characterized. Due to both the small cavity volume and the high refractive index of silicon we are able to tune resonances with extremely low mode index, whose electric field distribution resembles those of electronic orbitals. The value of some parameters such as quality factor Q, effective mode volume, and evanescent field have been calculated for several modes. This calculation indicates silicon colloids can be a serious strategy for developing optical microcavities where may coexist both optical modes with large evanescent fields useful for sensing applications, as well as modes with high Q/V ratio values, of the order of 10(9)(λ/n)(-3).

Colloidal crystal thin films grown into corrugated surface templates.

The influence of patterned surfaces on the formation of one- and two-dimensional colloidal crystals is analyzed. We have used the corrugated surface of a digital versatile disc (DVD) for template surface processing. When the sphere diameter is on the order of the groove width of patterned substrates, a rich variety of particle decorations appear. However, if particle size is much larger than template patterns, large domains of particle ordering are formed.

Photonic binding in silicon-colloid microcavities.

Photonic binding between two identical silicon-colloid-based microcavities is studied by using a generalized multipolar expansion. In contrast with previous works, we focus on low-order cavity modes that resemble low-energy electronic orbitals. For conservative light intensities, the interaction between cavity modes with moderate Q factors produces extremely large particle acceleration values. Optical forces dominate over van der Waals, gravity, and Brownian motion, and they show a binding-antibinding behavior in analogy to electronic binding. As these photonic forces are associated with relatively broad Mie mode resonances and they are not strongly influenced by sample absorption, our study opens a plausible avenue towards manipulation of high-refractive-index colloidal assemblies.

Dolor lumbar como manifestación inusual en una valvulopatía: ejemplo de dificultad en el diagnóstico etiológico de las lumbalgias crónicas / Lumbar pain as an uncommon manifestation of valvular disease: an example of the difficulty of etiologic diagnosis of chronic low back pain

La patología más frecuente en las unidades de dolor crónico es la lumbalgia. El diagnóstico diferencial entre las diferentes etiologías que pueden causarlo es, a menudo, difícil. Las comúnmente llamadas banderas rojas (red flags) de la lumbalgia son una serie de “signos-síntomas” que deben alertarnos acerca de la posibilidad de la gravedad del síntoma y han motivado múltiples trabajos. De la misma forma, nosotros, con la exposición de este caso clínico, queremos remarcar la necesidad de la realización de una detallada historia clínica y la revaluación de aquellos pacientes que vienen derivados de otras consultas con un diagnóstico previo, puesto que nos puede evitar errores de diagnóstico y tratamiento. Presentamos el caso de un enfermo de 55 años, remitido a la unidad de dolor crónico por medicina interna, con el diagnóstico de lumbalgia crónica, en tratamiento con analgésicos, sin respuesta eficaz. Durante los dos últimos años el paciente refería dolor en la zona dorsal baja y lumbar, de intensidad moderada/severa. Como antecedentes patológicos de interés había sido intervenido de una afección mitral, con la implantación de una válvula mecánica 17 años antes. Los episodios de dolor crónico se exacerbaban con crisis de dolor agudo en la zona dorsal baja irradiado a la región lumbar e inguinal. Aunque las crisis de anemia hemolítica aguda pueden cursar con dolor lumbar, este antecedente no se tuvo en cuenta como probable origen del dolor. En la resonancia magnética (RM) lumbarse apreciaban cambios degenerativos con polidiscopatía L4-L5, L5-S1 y signos de artrosis interapofisaria. El remplazo de la válvula protésica malfuncionante por una nueva finalizó con la hemólisis y el dolor lumbar. El paciente permanece asintomático un año después (AU)

Low back pain is the most frequent complaint in chronic pain units. The differential diagnosis among the distinct causes is frequently difficult. The “red flags” of low back pain consist of a series of “signs and symptoms” that should warn clinicians of the possibility of the severity of the symptom and have been the subject of numerous publications. The present case report aims to highlight the need to take a detailed clinical history and to reevaluate patients with a prior diagnosis referred by other services in order to avoid diagnostic and treatment errors. We present the case of a 55-year-old man, who was referred to the chronic pain clinic by the internal medicine service, with a diagnosis of chronic low back pain unresponsive to analgesics. For the previous 2 years, the patient had reported moderate-severe pain in the lower dorsal and lumbar region. Seventeen years previously, a prosthetic mitral valve had been implanted. The patient’s chronic pain episodes were exacerbated by crises of acute pain in the lower dorsal region radiating to the lumbar and inguinal areas. Although acute hemolytic anemia is described as an etiology of low back pain, this antecedent was not taken into account as a probable cause of the pain. Lumbar magnetic resonance imaging showed degenerative osteoarthritis. Replacement of the prosthetic valve resolved the lumbar pain and hemolysis. One year later, the patient remains asymptomatic (AU)

Abordaje del ganglio de Walter por vía transdiscal coccígea en coccigodina / Cocygeal transdiscal approach of ganglion impar for the treatment of coccygodynia

Objetivo Valorar la eficacia y seguridad del abordaje transdiscal coccígeo para el bloqueo con anestésicos locales y corticoides del ganglio de Walter en la coccigodinia. Pacientes y Método Estudiamos prospectivamente 6 pacientes, 4 mujeres (66´6%) y 2 hombres ( 33,4%) , con coccigodinia de más de 6 meses de duración, de origen benigno y puntuación media 6 en la escala analógica visual (EVA). Se llevó a cabo el abordaje del ganglio de Walter para su bloqueo (con anestésicos locales y corticoides) por vía transdiscal coccígea en quirófano. Se evaluó la eficacia analgésica, el grado de satisfacción y las complicaciones. Resultados Cinco de los seis pacientes, fueron dados de alta sin dolor (EVA<1). El total de la muestra manifestó estar satisfecho con el tratamiento. Tras cuatro meses de seguimiento, no registramos complicaciones. Conclusiones El abordaje transdiscal del ganglio de Walter es sencillo, seguro (con menos riesgo de perforación del recto y de inyección peri-ósea de la solución, que la vía clásica utilizada para su bloqueo) y eficaz en el tratamiento de la coccigodinia

Objetive To test the efficacy and safety of the Walter ganglion blockade trough coccygeal disc, in patients who suffered from coccygodynia. Patients and Methods We evaluated six patients, 4 women (66,6%) and two men (33,4%), with chronic coccyx pain (>6 months), and more than 6 points in Visual Analogue Scale (VAS). We described the trans-coccygeal disc approach to Walter ganglion blockade technique. The improvement of pain score, degree of satisfaction and complications of the patients were evaluated. Results Five patients improved VAS score 6 to 1. All the patients were satisfied with the treatment. We had no complications. Conclusions The trans-discal approach of the Walter ganglion is easy, safe (with less risk of rectal perforation and bone traumatism than the classical ano-coccygeal ligament via), and effective for chronic coccygodynia

Layering transitions in confined colloidal crystals: the hcp-like phase.

This paper investigates the sequence of morphological transitions in a nearly hard sphere arrangement confined in a wedge cell. A model that shows smooth transitions between the different particle orderings for a small number of layers is proposed. In this model, both the buckling and the (100) hexagonal close packed (hcp) phases are particular cases of a much more general particle arrangement tendency that we call hcp-like ordering. This phase, which does not correspond to any known close packed ordering, is able to adopt packing arrangements commensurate with the cell thickness. More striking, the hcp-like phase adapts itself to the progressive changes of the cell thickness by a smooth change in the interlayer spacing. We present hcp-like orderings up to six layers and a complete sequence of transformations between two and four layers. Finally, a packing model of the transition from two to three layers is also presented.

Faceting and commensurability in crystal structures of colloidal thin films.

This Letter investigates the influence of finite size effects on the particle arrangement of thin film colloidal crystals. A rich variety of crystallographic faceting with large single domain microcrystallites is shown. Optical reflectance experiments together with scanning electron microscopy permit the identification of the crystal symmetry and the facet orientation, as well as the exact number of monolayers. When the cell thickness is not commensurable with a high symmetry layering, particles arrange themselves in a periodic distribution of (111)- and (100)-orientated face centered cubic (fcc) microcrystallites separated by planar defects. These structures can be described as a fcc ordering orientated along a vicinal surface, modified by a periodic distribution of fcc (111) stacking faults.

Comment on "Theory of tailoring sonic devices: diffraction dominates over refraction".

Recently, Garcia et al. [Phys. Rev. E 67, 046606 (2003)] studied theoretically several acoustic devices with dimensions on the order of several wavelengths. Those authors also discussed experimental results previously reported by several of us [Phys. Rev. Lett. 88, 023902 (2002)]] and concluded that it is diffraction rather than refraction that is the dominating mechanism explaining the focusing effects observed in those experiments. In this Comment we reexamined their calculations and discussed why some of their interpretations of our results are misleading.

Refractive acoustic devices for airborne sound.

We show that a sonic crystal made of periodic distributions of rigid cylinders in air acts as a new material which allows the construction of refractive acoustic devices for airborne sound. It is demonstrated that, in the long-wave regime, the crystal has low impedance and the sound is transmitted at subsonic velocities. Here, the fabrication and characterization of a convergent lens are presented. Also, an example of a Fabry-Perot interferometer based on this crystal is analyzed. It is concluded that refractive devices based on sonic crystals behave in a manner similar to that of optical systems.

Single dose dipyrone for acute renal colic pain.

BACKGROUND: Renal colic pain is extremely painful and requires immediate treatment with strong analgesics. Dipyrone is the most popular non-opioid first line analgesic in many countries but in others it has been banned (e.g. USA, UK) because of its association with blood dyscrasias such as agranulocytosis. Since dipyrone is used in many countries (e.g. Brazil, Spain) there is a need to determine the benefits and harms of its use to treat renal colic pain. OBJECTIVES: To assess quantitatively the analgesic efficacy and adverse effects of single-dose dipyrone in adults with moderate to severe renal colic pain. SEARCH STRATEGY: Published reports were identified from electronic databases (MEDLINE, EMBASE, the Cochrane Library, LILACS) and additional studies were identified from the reference lists of retrieved reports. Date of the most recent search: January 2000. SELECTION CRITERIA: Inclusion criteria were: full journal publication; RCT with a double-blind design; adult patients with baseline renal colic pain of moderate or severe intensity; treatment arms which included dipyrone (oral, intramuscular or intravenous administration) and a control; single dose data. DATA COLLECTION AND ANALYSIS: Summed pain intensity and pain relief data were extracted and converted into dichotomous information to yield the number of patients with at least 50% pain relief over 15-30 minutes, 1-2 hours and six hours. The proportion of patients with at least 50% pain relief was calculated. Single dose adverse effect data were collected. MAIN RESULTS: Eleven studies with 1053 patients (550 on dipyrone) met the inclusion criteria. Unfortunately, few data were available for analysis; most analyses were based on the results of single, small trials and statistical pooling of the results was inappropriate. Efficacy estimates were calculated as the weighted mean percent of patients achieving at least 50% pain relief with the range of values from trials contributing to the analysis. However, these estimates were not robust. Commonly reported adverse effects with intravenous dipyrone were dry mouth and somnolence, and one study reported pain at the injection site. Insufficient information was available for safety analyses to be conducted. REVIEWER'S CONCLUSIONS: Limited available data indicated that single dose dipyrone was of similar efficacy to other analgesics used in renal colic pain, although intramuscular dipyrone was less effective than diclofenac 75 mg. Combining dipyrone with antispasmolytic agents did not appear to improve its efficacy. Intravenous dipyrone was more effective than intramuscular dipyrone. Dry mouth and somnolence were commonly reported with intravenous dipyrone. None of the studies reported agranulocytosis.

Single-dose dipyrone for acute postoperative pain.

BACKGROUND: The use of dipyrone as an analgesic is controversial. It is used most commonly to treat postoperative pain, colic pain, cancer pain and migraine, and in many countries, eg, Russia, Spain, Brazil, and in many parts of South-America and Africa, it is the most popular non opioid first line analgesic. In others it has been banned (e.g. USA, UK) because of its association with potentially life-threatening blood dyscrasias such as agranulocytosis. Dipyrone is currently available in Austria, Belgium, France, Germany, Italy, The Netherlands, Spain, Switzerland, South Africa, Latin America, Russia, Israel and India. OBJECTIVES: To assess quantitatively the analgesic efficacy and adverse effects of single-dose dipyrone in randomised trials in moderate to severe postoperative pain. To compare the relative efficacy of dipyrone with other drugs assessed in the same way. SEARCH STRATEGY: Published reports were identified from Medline, Embase, the Cochrane Library (Issue 3 1999), LILACs and the Oxford Pain Relief Database. Additional studies were identified from bibliographies of retrieved reports. Date of the most recent search: December 1999. SELECTION CRITERIA: The following inclusion criteria were used: full journal publication, clinical trial, random allocation of patients to treatment groups, double-blind design, adult patients, pain of moderate to severe intensity at the baseline assessment, postoperative administration of study drugs, treatment arms which included dipyrone and placebo or active control and oral, rectal, intramuscular or intravenous administration of study drugs. DATA COLLECTION AND ANALYSIS: Summed pain intensity and pain relief data over 4-6 hours were extracted and converted into dichotomous information to yield the number of patients who obtained at least 50% pain relief. This was used to calculate the proportion of patients with, and number-needed-to-treat for, at least 50% pain relief over 4-6 hours. Single-dose adverse effect data were collected. MAIN RESULTS: Fifteen studies were included; eight used placebo and seven used an active control (oral dexketoprofen 12.5 mg or 25 mg, oral ketorolac 10 mg, intramuscular pethidine 100 mg or ketorolac 30 mg, intravenous tramadol 100 mg or rectal suprofen 300 mg). In five trials (288 patients) the mean response rate (proportion of patients with at least 50% pain relief) for single dose oral dipyrone 500 mg was 73% (range 54% to 87%) and with placebo it was 32% (19% to 41%) in moderate to severe postoperative pain over 4-6 hours. In two studies (113 patients) the response rate with oral dipyrone 1 g was 69% (61% and 77%) and with placebo it was 20% (11% and 25%). In one study (70 patients) the response rate with intramuscular dipyrone 2 g was 74% and with placebo it was 46%. No analyses could be conducted for adverse effects. The response rates in the active controlled trials were similar to those reported in the placebo controlled trials. REVIEWER'S CONCLUSIONS: Single-dose dipyrone appears to be of similar efficacy to ibuprofen 400 mg and other analgesics frequently used in the treatment of moderate to severe postoperative pain. The commonest adverse effects were somnolence, gastric discomfort and nausea.

Three-Dimensional Arrays Formed by Monodisperse TiO(2) Coated on SiO(2) Spheres.

Uniform coatings of TiO(2) on monodisperse spheres of silica have been obtained. The resulting particle sizes are within the range 0.4 to 1 µm. The thickness of the coating can be controlled by adjusting nuclei sizes (silica sphere), reaction times, and water and surfactant concentrations. The TiO(2)/SiO(2) spheres were sedimented to achieve structures with three-dimensional order. Three-dimensional ordered materials with higher refractive index were obtained by transforming the amorphous titania layer to rutile by thermal treatment with improved mechanical rigidity. The sphere composition, quality, and morphology have been assessed by different techniques. Copyright 2000 Academic Press.

Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres

Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 microm, produced by growing silicon inside the voids of an opal template of dose-packed silica spheres that are connected by small 'necks' formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Metaanálisis en dolor / Pain metaanalysis

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Large two-dimensional sonic band gaps.

We show that absolute sonic band gaps produced by two-dimensional square and triangular lattices of rigid cylinders in air can be increased by reducing the structure symmetry. In the case of square lattices, symmetry reduction is achieved by a smaller diameter cylinder placed at the center of each unit cell. For triangular lattices the reduction is achieved by decreasing the diameter of the cylinder at the center of the hexagons in the lattice. Theoretical predictions are also demonstrated experimentally: starting from a honeycomb lattice (using cylinders of 4 cm of diameter size and 6.35 cm nearest-neighbor distance) we have studied the transition to a triangular symmetry by putting rods with increasing diameter (in the range 0.6-4 cm) at the center. The greatest enhancement of the attenuation strength observed in transmission experiments has been obtained in the high frequency region for diameter ratios in the range 0.1-0.3.