Weber number and the outcome of binary collisions between quantum droplets.

A theoretical analysis of binary collisions of quantum droplets under feasible experimental conditions is reported. Droplets formed from degenerate dilute Bose gases made up from binary mixtures of ultracold atoms are considered. Reliable expressions for the surface tension of the droplets are introduced based on a study of low energy excitations of their ground state within the random phase approximation. Their relevance is evaluated considering an estimation of the expected excitation energy having in mind the Thouless variational theorem. The surface tension expressions allow calculating the Weber number of the droplets involved in the collisions. Several regimes on the outcomes of the binary frontal collisions that range from the coalescence of the quantum droplets to their disintegration into smaller droplets are identified. Atoms losses of the droplets derived from self-evaporation and three-body scattering are quantified for both homo- and hetero-nuclear mixtures. Their control is mandatory for the observation of some interesting effects arising from droplets collisions.

Ecotoxicological risk assessment in soils contaminated by Pb and As 20 years after a mining spill.

This study evaluates the potential toxicity of the soils of the Guadiamar Green Corridor (GGC) affected by the Aznalcóllar mine spill (Andalusia, Spain), one of the most important mining accidents in Europe in recent decades. Twenty years after the accident, although the area is considered to be recovered, residual contamination in soils persists, and the bioavailability of some contaminants, such as As, is showing trends of increasing. Therefore, the potential residual toxicity in 84 soil samples was evaluated by bioassays with lettuce (Latuca sativa L.), earthworms (Eisenia andrei) and determining the microbial activity by basal respiration and metabolic quotient. The selected soils sampled along the GGC were divided into 4 types according to their physicochemical properties. In the closest part of the mine two soil types appear (SS1 and SS2), originally decarbonated and loamy, with a reduction in lettuce root elongation of 57% and 34% compared to the control, as well as a the highest metabolic quotient (23.9 and 18.1 ng CcO2 µg Cmicrob-1 h-1, respectively) with the highest risk of Pb and As toxicity. While, located in the middle and final part of the affected area of the spill (SS3 and SS4), soils presented alkaline pH, finer textures and the lowest metabolic quotient (<9.5 ng CcO2 µg Cmicrob-1 h-1). In addition, due to Pb and As exceeded the Guideline values established in the studied area, the human toxicity risk was determined according to US-EPA methodology. Although the total contents were higher than the Guidelines established, the obtained hazard quotients for both contaminants were less than one, so the risk for human health was discarded. However, monitoring over time of the toxicity risks of the GGC soils would be advisable, especially due to the existence of areas where residual contamination persist, and soil hazard quotient obtained for As in children was higher and close to unity.

Control of Localized Single- and Many-Body Dark States in Waveguide QED.

Subradiant states in a finite chain of two-level quantum emitters coupled to a one-dimensional reservoir are a resource for superior photon storage and their controlled release. As one can maximally store one energy quantum per emitter, storing multiple excitations requires delocalized states, which typically exhibit fermionic correlations and antisymmetric wave functions, thus making them hard to access experimentally. Here we identify a new class of quasilocalized dark states with up to half of the qubits excited, which only appear for lattice constants of an integer multiple of the wavelength. These states allow for a high-fidelity preparation and minimally invasive readout in state-of-the-art setups. In particular, we suggest an experimental implementation using a coplanar waveguide coupled to superconducting transmon qubits on a chip. With minimal free space and intrinsic losses, virtually perfect dark states can be achieved for a low number of qubits featuring fast preparation and precise manipulation.

Morphologies of caustics and dislocation lines: some clues about their interrelation.

According to singular optics, the phase and intensity that characterize structured electromagnetic beams can be understood in terms of concepts that involve subspaces where they or their derivatives exhibit a particular behavior, such as giving rise to extreme values or not being well defined. Caustics are a paradigmatic example of the former, while helical dislocation lines exemplify the latter. In this work the interrelation of the morphology of caustics and the morphology of dislocation lines is theoretically studied. The analysis for highly structured beams requires an efficient methodology that allows the identification of optical vortices, their topological charge, and the helical dislocation lines they belong to. Such a methodology is introduced and applied to paraxial elliptic umbilic beams and nonparaxial Airy symmetric three-dimensional beams. Nonparaxial beams exhibit caustic surfaces that delimit regions with a finite volume and different intensity average. It is shown that in the high intensity region so defined, the dislocation lines play the role of an internal skeleton, i.e., an endoskeleton, of the beam. The exoskeleton created in the low intensity regions shows subtle and interesting features that complement those of the endoskeleton; the caustics that delimit low intensity regions have a strong influence on the morphology of the exoskeleton.

Multisystem combined uranium resistance mechanisms and bioremediation potential of Stenotrophomonas bentonitica BII-R7: Transcriptomics and microscopic study.

The potential use of microorganisms in the bioremediation of U pollution has been extensively described. However, a lack of knowledge on molecular resistance mechanisms has become a challenge for the use of these technologies. We reported on the transcriptomic and microscopic response of Stenotrophomonas bentonitica BII-R7 exposed to 100 and 250 µM of U. Results showed that exposure to 100 µM displayed up-regulation of 185 and 148 genes during the lag and exponential phases, respectively, whereas 143 and 194 were down-regulated, out of 3786 genes (>1.5-fold change). Exposure to 250 µM of U showed up-regulation of 68 genes and down-regulation of 290 during the lag phase. Genes involved in cell wall and membrane protein synthesis, efflux systems and phosphatases were up-regulated under all conditions tested. Microscopic observations evidenced the formation of U-phosphate minerals at membrane and extracellular levels. Thus, a biphasic process is likely to occur: the increased cell wall would promote the biosorption of U to the cell surface and its precipitation as U-phosphate minerals enhanced by phosphatases. Transport systems would prevent U accumulation in the cytoplasm. These findings contribute to an understanding of how microbes cope with U toxicity, thus allowing for the development of efficient bioremediation strategies.

Spontaneous transition rates near the focus of a parabolic mirror with identification of the vectorial modes involved.

Each natural mode of the electromagnetic field within a parabolic mirror exhibits spatial localization and polarization properties that can be exploited for the quantum control of its interaction with atomic systems. The region of localization is not restricted to the focus of the mirror leading to a selective response of atomic systems trapped on its vicinity. We report calculations of the spontaneous emission rates for an atom trapped inside the mirror accounting for all atomic polarizations and diverse trapping regions. It is shown that electric dipole transitions can be enhanced near the focus of a deep parabolic mirror with a clear identification of the few vectorial modes involved. Out of the focus the enhancement vanishes gradually, but the number of relevant modes remains small. Ultimately this represents a quantum electrodynamic system where internal and external degrees of freedom cooperate to maximize a selective exchange and detection of single excitations.

To catch and reverse a quantum jump mid-flight.

In quantum physics, measurements can fundamentally yield discrete and random results. Emblematic of this feature is Bohr's 1913 proposal of quantum jumps between two discrete energy levels of an atom1. Experimentally, quantum jumps were first observed in an atomic ion driven by a weak deterministic force while under strong continuous energy measurement2-4. The times at which the discontinuous jump transitions occur are reputed to be fundamentally unpredictable. Despite the non-deterministic character of quantum physics, is it possible to know if a quantum jump is about to occur? Here we answer this question affirmatively: we experimentally demonstrate that the jump from the ground state to an excited state of a superconducting artificial three-level atom can be tracked as it follows a predictable 'flight', by monitoring the population of an auxiliary energy level coupled to the ground state. The experimental results demonstrate that the evolution of each completed jump is continuous, coherent and deterministic. We exploit these features, using real-time monitoring and feedback, to catch and reverse quantum jumps mid-flight-thus deterministically preventing their completion. Our findings, which agree with theoretical predictions essentially without adjustable parameters, support the modern quantum trajectory theory5-9 and should provide new ground for the exploration of real-time intervention techniques in the control of quantum systems, such as the early detection of error syndromes in quantum error correction.

La tomografía computarizada corporal como factor asociado a menor mortalidad en el traumatismo geriátrico grave con afectación toracoabdominopélvica / Whole-body computed tomography as a factor associated with lower mortality in severe geriatric trauma with thoracic-abdominal-pelvic injury

Objetivo: Analizar la asociación de la realización de una tomografía computarizada (TC) corporal con la mortalidad intrahospitalaria en pacientes de edad avanzada con afectación toracoabdominopélvica que precisa ingreso en una unidad de cuidados intensivos. Pacientes y método: Estudio observacional, descriptivo y retrospectivo realizado sobre 140 pacientes con edad igual o mayor de 65 años ingresados en una unidad de cuidados intensivos tras un traumatismo con afectación toracoabdominopélvica. Se establecen 2 grupos, según se haya realizado TC corporal como parte rutinaria del estudio o el diagnóstico se estableciera mediante radiografía convencional o ecografía. Análisis comparativo de ambos grupos y análisis de la mortalidad mediante regresión logística. Resultados: La edad media fue de 75,16±8,89 años. La puntuación media en la escala APACHE II fue de 16,25±8,4 puntos, y en la escala Injury Severity Score, de 22,38±15,45 puntos. Se realizó TC corporal en 102 pacientes (72,9%). En estos se observó una menor mortalidad (15,7 frente a 52,6%; p¿0,001), una menor necesidad de ventilación mecánica (47,1 frente a 65,8%; p=0,049) y una menor puntuación en la escala APACHE II (14,75±7,19 frente a 20,26±10,06 puntos; p=0,003). El análisis multivariante mostró una menor mortalidad en los pacientes en los que se realizó TC corporal, con una OR de 0,21 (IC 95% 0,07-0,68; p=0,010), tras ajustar por puntuación en la escala APACHE II y en el Injury Severity Score. Conclusiones: La realización de TC corporal como parte del estudio del traumatismo podría mejorar el manejo de los pacientes de edad avanzada con afectación toracoabdominopélvica que ingresan en una unidad de cuidados intensivos

Objective: To determine the relationship between the use of whole-body computed tomography (WB-CT) and hospital mortality in elderly patients with thoracic-abdominal-pelvic injury requiring admission to an intensive care unit. Patients and method: An observational, descriptive and retrospective study was conducted on 140 patients aged 65 years and older admitted to the intensive care unit after a thoracic-abdominal-pelvic injury. Two groups were established, depending on whether a WB-CT was performed as a routine part of the study or the diagnosis was established by conventional radiography or ultrasound. A comparative analysis was performed on both groups, as well as an analysis of mortality through logistic regression. Results: The mean age of the patients was 75.16±8.89 years. The mean score on the APACHE II scale was 16.25±8.4 points, and on the Injury Severity Score scale, 22.38±15.45 points. WB-CT was performed on 102 patients (72.9%). In these patients, there was a lower mortality rate (15.7 vs. 52.6%, P¿.001), a lower need for mechanical ventilation (47.1 vs. 65.8%, P=.049), and a lower score on the APACHE II scale (14.75±7.19 vs. 20.26±10.06 points, P=.003). The multivariate analysis showed a lower mortality in the patients in whom WB-CT was performed, with an OR of 0.21 (95% CI 0.07-0.68; (P=.010), after adjusting for the APACHE II and ISS scores. Conclusions: Performing a WB-CT scan as part of the trauma study could improve the management of elderly patients with thoracic-abdominal-pelvic involvement admitted to the intensive care unit

Whole-body computed tomography as a factor associated with lower mortality in severe geriatric trauma with thoracic-abdominal-pelvic injury. / La tomografía computarizada corporal como factor asociado a menor mortalidad en el traumatismo geriátrico grave con afectación toracoabdominopélvica.

OBJECTIVE: To determine the relationship between the use of whole-body computed tomography (WB-CT) and hospital mortality in elderly patients with thoracic-abdominal-pelvic injury requiring admission to an intensive care unit. PATIENTS AND METHOD: An observational, descriptive and retrospective study was conducted on 140 patients aged 65 years and older admitted to the intensive care unit after a thoracic-abdominal-pelvic injury. Two groups were established, depending on whether a WB-CT was performed as a routine part of the study or the diagnosis was established by conventional radiography or ultrasound. A comparative analysis was performed on both groups, as well as an analysis of mortality through logistic regression. RESULTS: The mean age of the patients was 75.16±8.89 years. The mean score on the APACHE II scale was 16.25±8.4 points, and on the Injury Severity Score scale, 22.38±15.45 points. WB-CT was performed on 102 patients (72.9%). In these patients, there was a lower mortality rate (15.7 vs. 52.6%, P˂.001), a lower need for mechanical ventilation (47.1 vs. 65.8%, P=.049), and a lower score on the APACHE II scale (14.75±7.19 vs. 20.26±10.06 points, P=.003). The multivariate analysis showed a lower mortality in the patients in whom WB-CT was performed, with an OR of 0.21 (95% CI 0.07-0.68; (P=.010), after adjusting for the APACHE II and ISS scores. CONCLUSIONS: Performing a WB-CT scan as part of the trauma study could improve the management of elderly patients with thoracic-abdominal-pelvic involvement admitted to the intensive care unit.

In vitro colonisation of the distal colon by Akkermansia muciniphila is largely mucin and pH dependent.

Host mucin is the main constituent of the mucus layer that covers the gut epithelium of the host, and an important source of glycans for the bacteria colonising the intestine. Akkermansia muciniphila is a mucin-degrading bacterium, abundant in the human gut, that is able to produce acetate and propionate during this degradation process. A. muciniphila has been correlated with human health in previous studies, but a mechanistic explanation is lacking. In this study, the main site of colonisation was characterised alongside additional conditions, such as differences in colon pH, prebiotic supplementation and variable mucin supply. To overcome the limitations of in vivo studies concerning variations in mucin availability and difficult access to proximal regions of the colon, a dynamic in vitro gut model (SHIME) was used. In this model, A. muciniphila was found to colonise the distal colon compartment more abundantly than the proximal colon ((±8 log copies/ml compared to ±4 log copies/ml) and the preference for the distal compartment was found to be pH-dependent. The addition of mucin caused a specific increase of A. muciniphila (±4.5 log increase over two days), far exceeding the response of other bacteria present, together with an increase in propionate. These findings suggest that colonisation and mucin degradation by A. muciniphila is dependent on pH and the concentration of mucin. Our results revealed the preference of A. muciniphila for the distal colon environment due to its higher pH and uncovered the quick and stable response of A. muciniphila to mucin supplementation.

Efectos del retraso y la inadecuación del tratamiento antibiótico en la supervivencia de los pacientes en shock séptico / Effects of antibiotic administration delay and inadequacy upon the survival of septic shock patients

OBJETIVO: Evaluar cómo influye el retraso en la administración de la primera dosis de antibiótico y la inadecuación de la pauta seleccionada en la supervivencia de los pacientes en shock séptico. DISEÑO: Estudio prospectivo de cohortes observacional realizado entre septiembre de 2005 y septiembre de 2010. ÁMBITO: Pacientes hospitalizados en la UCI de un hospital de tercer nivel. PACIENTES: Trescientos cuarenta y dos pacientes con cuadro de shock séptico. INTERVENCIONES: Ninguna. Variables de interés principales: Se determinó el tiempo hasta la administración del antibiótico (diferencia entre la presentación del shock séptico y la primera dosis de antibiótico) y la adecuación del mismo (susceptibilidad in vitro de los microorganismos aislados). RESULTADOS: La mortalidad en UCI fue del 26,4% y a nivel hospitalario del 33,5%. La mediana de retraso en la administración de la primera dosis de tratamiento antibiótico fue de 1,7 h. Los pacientes fallecidos recibieron el antibiótico significativamente más tarde (1,3 ± 14,5 h frente a 5,8 ± 18,02; p = 0,001) que los supervivientes. El porcentaje de inadecuación del tratamiento antibiótico fue del 12%. Los pacientes tratados inadecuadamente presentaron cifras de mortalidad hospitalaria significativamente más altas (33,8% frente a 51,2%; p = 0,03) respecto a los que recibieron una pauta antibiótica adecuada. La coexistencia de retraso e inadecuación en el tratamiento antibiótico se asoció a una menor supervivencia de los pacientes. CONCLUSIONES: Tanto el retraso como la inadecuación del tratamiento antibiótico tienen efectos negativos sobre la supervivencia de los pacientes en shock séptico independientemente de las características de estos o de su estado de gravedad

OBJECTIVE: To assess how antibiotic administration delay and inadequacy influence survival in septic shock patients. DESIGN: A prospective, observational cohort study was carried out between September 2005 and September 2010. SCOPE: Patients admitted to the ICU of a third level hospital. PATIENTS: A total of 342 septic shock patients Interventions: None Variables of interest: The time to antibiotic administration (difference between septic shock presentation and first administered dose of antibiotic) and its adequacy (in vitro susceptibility testing of isolated pathogens) were determined. RESULTS: ICU and hospital mortality were 26.4% and 33.5%, respectively. The median delay to administration of the first antibiotic dose was 1.7 h. Deceased patients received antibiotics significantly later than survivors (1.3 ± 14.5 h vs. 5.8 ± 18.02 h; P = .001). Percentage drug inadequacy was 12%. Those patients who received inadequate antibiotics had significantly higher mortality rates (33.8% vs. 51.2%; P = .03). The coexistence of treatment delay and inadequacy was associated to lower survival rates. CONCLUSIONS: Both antibiotic administration delay and inadequacy exert deleterious effects upon the survival of septic shock patients, independently of their characteristics or severity

Effects of antibiotic administration delay and inadequacy upon the survival of septic shock patients.

OBJECTIVE: To assess how antibiotic administration delay and inadequacy influence survival in septic shock patients. DESIGN: A prospective, observational cohort study was carried out between September 2005 and September 2010. SCOPE: Patients admitted to the ICU of a third level hospital. PATIENTS: A total of 342 septic shock patients INTERVENTIONS: None VARIABLES OF INTEREST: The time to antibiotic administration (difference between septic shock presentation and first administered dose of antibiotic) and its adequacy (in vitro susceptibility testing of isolated pathogens) were determined. RESULTS: ICU and hospital mortality were 26.4% and 33.5%, respectively. The median delay to administration of the first antibiotic dose was 1.7h. Deceased patients received antibiotics significantly later than survivors (1.3±14.5h vs. 5.8±18.02h; P=.001). Percentage drug inadequacy was 12%. Those patients who received inadequate antibiotics had significantly higher mortality rates (33.8% vs. 51.2%; P=.03). The coexistence of treatment delay and inadequacy was associated to lower survival rates. CONCLUSIONS: Both antibiotic administration delay and inadequacy exert deleterious effects upon the survival of septic shock patients, independently of their characteristics or severity.

On the general properties of symmetric incomplete Airy beams.

We study the general properties of a class of Airy beams symmetric under reflection of the transverse coordinates. Following a recent proposal, their angular spectra depend on the absolute value of the third power of the transverse components of the wave vector. The proposed beams are shown to be described by symmetric superpositions of incomplete Airy special functions. Their angular spectra do not correspond to any of those described by standard catastrophe optics. However, the morphologies of the symmetric beams are similar to some of those already classified within that scheme, differing mainly on the scaling exponents. Finally, the structural stability of three-dimensional symmetric incomplete Airy beams is experimentally probed.

Nonlinear magnetotransport theory and Hall induced resistance oscillations in graphene.

The quantum oscillations of nonlinear magnetoresistance in graphene that occur in response to a dc current bias are investigated. We present a theoretical model for the nonlinear magnetotransport of graphene carriers. The model is based on the exact solution of the effective Dirac equation in crossed electric and magnetic fields, while the effects of randomly distributed impurities are perturbatively added. To compute the nonlinear current effects, we develop a covariant formulation of the migration center theory. The current is calculated for short- and large-range scatterers. The analysis of the differential resistivity in the large magnetic field region, shows that the extrema of the Shubnikov de Hass oscillations invert when the dc currents exceed a threshold value. These results are in good agreement with experimental observations. In the small magnetic field regime, corresponding to large filling factors, the existence of Hall induced resistance oscillations are predicted for ultra clean graphene samples. These oscillations originate from Landau-Zener tunneling between Landau levels, that are tilted by the strong electric Hall field.

Renal calcium, phosphorus, magnesium and uric acid handling: comparison between stage III chronic kidney disease patients and healthy oldest old.

INTRODUCTION: It is known that chronic kidney disease (CKD) and senescence bring about a progressive reduction in glomerular filtration rate (GFR) and that in the former this is usually associated with an increase in the fractional excretion of calcium, phosphorus, magnesium, and uric acid. However, it has not yet been explained how these substances are excreted in the healthy oldest old. Thus, in the present study, we examined the renal handling of these substances in very aged people in comparison with CKD patients with similar GFR levels (stage III-CKD). MATERIALS AND METHODS: Twenty volunteers were studied; 10 of them were healthy very old (VO) (≥ 75 years old) individuals and 10 were stage III CKD patients. Exclusion criteria were as follows: presence of altered (abnormally high or low) plasma calcium, phosphorus, magnesium and uric acid, as well as previous diagnoses of diabetes mellitus and obstructive uropathy and use of drugs that could alter plasma levels of the studied substances. All volunteers were on a diet with the same content of these elements (3-day dietary register). We measured calcium, phosphorus, magnesium, uric acid, creatinine in serum plasma and morning urine, as well as serum parathyroid hormone level, in each volunteer. From these data, fractional excretion (FE) of these substances was obtained. A statistical analysis was carried out using the Wilcoxon test. RESULTS: Serum creatinine: 1.8 ± 0.4 mg/dl (CKD) versus 0.8 ± 0.2 mg/dl (VO), p = 0.0002; serum calcium: 9.1 ± 0.3 mg/dl (CKD) versus 8.7 ± 0.4 (VO), p = 0.022; serum magnesium: 2.3 ± 0.2 mg/dl (CKD) versus 2.0 ± 0.1 (VO), p = 0.05; serum phosphorus: 3.9 ± 0.5 mg/dl (CKD) versus 3.0 ± 0.4 mg/dl (VO), p = 0.002; serum uric acid: 6.6 ± 1.5 (CKD) versus 5.2 ± 1.4 mg/dl (VO), p = 0.04; FE of calcium: 2.5 ± 1 % (CKD) versus 0.8 ± 0.3 % (VO), p = 0.04; FE of magnesium: 7.2 ± 4.1 % (CKD) versus 2.9 ± 0.9 % (VO), p = 0.02; FE of phosphorus: 25 ± 9 % (CKD) versus 9.1 ± 5.7(VO), p = 0.001; FE of uric acid: 10 ± 3 % (CKD) versus 8 ± 5 % (VO), p = 0.05. CONCLUSION: Serum levels and FE of calcium, phosphorus, magnesium and uric acid were significantly higher in CKD patients compared to healthy very old people with similar GFR, except for serum magnesium and FE of uric acid, which were similar in both groups.

The value of a formula including haematocrit, blood urea and gender (HUGE) as a screening test for chronic renal insufficiency.

INTRODUCTION: Despite increasing use in clinical practice, an estimated glomerular filtration rate value (eGFR) of <60 ml/min/1.73 m2 does not necessarily indicate the existence of chronic renal insufficiency (CRI) and this may lead to an over-estimate of CRI particularly in persons seventy years or older. AIM: To find a screening test able to differentiate CRI from the decrease in GFR normally associated with the renal ageing process. METHODS: Medical information of 487 individuals of both sexes aged 16-102 was obtained from nephrologists, internal medicine physicians, cardiologists, geriatricians, family and nuclear medicine doctors from Argentina, Portugal and Spain. Data were assessed and statistically analysed using logistic regression techniques. From the discriminative variables it was derived the HUGE formula. RESULTS: A formula including haematocrit , blood urea, and gender (HUGE), diagnoses CRI regardless of the variables of age, blood creatinine, creatinine clearance, or other eGFR. The HUGE formula is: L = 2.505458 - (0.264418 x Hematocrit) + (0.118100 x Urea) [+ 1.383960 if male]. If L is a negative number the individual does not have CRI; if L is a positive number, CRI is present. Our data demonstrate that the HUGE formula is more reliable than MDRD and CKD-EPI, particularly in persons aged over 70. CONCLUSIONS: Our HUGE screening formula offers a straightforward, easily available and inexpensive method for differentiating between CRI and eGFR < 60 ml/min/1.73 m2 that will prevent a considerable number of aged healthy persons, as much as 1.700.000 in Spain and 2.600.000 in U.K., to be excluded from clinical assays or treatments contraindicated in CRI.

Experimental generation and analysis of first-order TE and TM Bessel modes in free space.

We demonstrate the experimental generation at optical frequencies of the lowest- and first-order Bessel beams with TE and TM polarizations in free space by means of a Mach-Zehnder interferometer. The polarization and angular momentum properties of these waves are analyzed and discussed.

Genome analysis of Escherichia coli promoter sequences evidences that DNA static curvature plays a more important role in gene transcription than has previously been anticipated.

We have performed a computer analysis to study the prevalence of DNA static curvature in the regulatory regions of Escherichia coli, detecting a large number of operons with curved DNA fragments in their 5' upstream regions. A statistical analysis reveals that all the global transcription factors identified so far in E. coli have a tendency to regulate operons with curved DNA sequences in their upstream regions. In addition to these global regulators, we also found that the PurR, ArgR, FruR, TyrR, and CytR specific regulators present a similar propensity. Interestingly, for these cases we found no previous reference describing a possible relationship with curved DNA regions. To validate our theoretical results, we performed site-directed mutagenesis to reduce the degree of DNA curvature in the regulatory sequences of the aroG, pyrC, and argCBH operons. The effects of these changes were measured by polyacrylamide gel electrophoresis assays and further evaluated in vivo by transcriptional fusions to a reporter gene. All our results point toward a more widespread role of curved DNA in gene transcription, a fact that has previously been underestimated.

Mie scattering and the physical mechanisms of sonoluminescence

We propose an experimental procedure to investigate possible mechanisms for radiation emission in sonoluminescence. Our analysis is based on Mie's theory of light scattering for a coated sphere in an external medium. Depending on the physical mechanism responsible of sonoluminescence, the dielectric constant of the hot spot changes. As a case study we consider the problem of the detection of an inner plasma core in sonoluminescent bubbles. Our results show that polarization measurements of scattered light should discern the presence of a plasma provided that light detectors are fast enough. Extensions to other emission mechanisms are briefly discussed.