Solving the mystery of booming sand dunes

Desert booming can be heard after a natural slumping event or during a sand avalanche generated by humans sliding down the slip face of a large dune. The sound is remarkable because it is composed of one dominant audible frequency (70 to 105 Hz) plus several higher harmonics. This study challenges earlier reports that the dunes’ frequency is a function of average grain size by demonstrating through extensive field measurements that the booming frequency results from a natural waveguide associated with the dune. The booming frequency is fixed by the depth of the surficial layer of dry loose sand that is sandwiched between two regions of higher compressional body wave velocity. This letter presents measurements of the booming frequencies, compressional wave velocities, depth of surficial layer, along with an analytical prediction of the frequency based on constructive interference of propagating waves generated by avalanching along the dune surface

Reply to comment by B. Andreotti et al. on "Solving the mystery of booming sand dunes"

This reply addresses three main issues raised in the comment of Andreotti et al. [2008]. First, the turning of ray paths in a granular material does not preclude the propagation of body waves and the resonance condition described by Vriend et al. [2007]. The waveguide model still holds in the dune for the observed velocities, even with a velocity increase with depth as implied by Andreotti et al. [2008]. Secondly, the method of initiation of spontaneous avalanching does not influence the booming frequency. The frequency is independent of the source once sustained booming starts; it depends on the subsurface structure of the dune. Thirdly, if all data points from Vriend et al. [2007] are included in the analysis (and not an average or selection), no correlation is observed between the sustained booming frequency and average particle diameter

High Gain Amplifier with Enhanced Cascoded Compensation

A two-stage CMOS operational amplifier with both, gain-boosting and indirect current feedback frequency compensation performed by means of regulated cascode amplifiers, is presented. By using quasi-floating-gate transistors (QFGT) the supply requirements, the number of capacitors and the size of the compensation capacitors respect to other Miller schemes are reduced. A prototype was fabricated using a 0.5 μm technology, resulting, for a load of 45 pF and supply voltage of 1.65 V, in open-loop-gain of 129 dB, 23 MHz of gain-bandwidth product, 60o phase margin, 675 μW power consumption and 1% settling time of 28 ns

Lymphotoxins and cytomegalovirus cooperatively induce interferon-beta, establishing host-virus détente

Tumor necrosis factor (TNF)-related cytokines regulate cell death and survival and provide strong selective pressures for viruses, such as cytomegalovirus (CMV), to evolve counterstrategies in order to persist in immune-competent hosts. Signaling by the lymphotoxin (LT)-β receptor or TNF receptor-1, but not Fas or TRAIL receptors, inhibits the cytopathicity and replication of human CMV by a nonapoptotic, reversible process that requires nuclear factor κB (NF-κB)-dependent induction of interferon-β (IFN-β). Efficient induction of IFN-β requires virus infection and LT signaling, demonstrating the need for both host and viral factors in the curtailment of viral replication without cellular elimination. LTα-deficient mice and LTβR-Fc transgenic mice were profoundly susceptible to murine CMV infection. Together, these results reveal an essential and conserved role for LTs in establishing host defense to CMV

Optimización de los parámetros de operación en un proceso de tratamiento de aguas por electro-oxidación

En este estudio se evaluó la electro-oxidación como tratamiento para aguas residuales provenientes del proceso de producción de resinas fenólicas. Los experimentos se llevaron a cabo en un reactor tipo batch a escala laboratorio con una configuración monopolar con electrodos de grafito y titanio. Se realizaron ensayos preliminares con un volumen de muestra de 200 ml, un área sumergida de 25.13 cm2 para el electrodo de grafito (ánodo) y 40 cm2 para el electrodo de titanio (cátodo) y un tiempo de residencia de 240 minutos, 15 voltios y una agitación de 200 rpm.113 p.This study evaluated the electro-oxidation of phenolic resins production wastewater treatment. The experiments were carried out in a laboratory scale batch reactor with a monopolar configuration was built with graphite (anode) and titanium (cathode) electrodes. Prelimary tests were carried out with a sample volume of 200 ml, a submerged area of 25.13 cm2 for the graphite electrode and 40 cm2 for the titanium electrode and 240 minutes as a residence time, voltage of 15 V and an agitation value of 200 rpm.Contenido parcial: Aguas contaminadas con fenol -- Procesos electroquímicos de oxidación avanzada -- Electro-Oxidación -- Aspectos técnicos de operación de la electro-oxidación -- Especificaciones técnicas de la celda para electro-oxidación -- Diseño de experimentos