The effects of cochlear hypothermia on compound action potential tuning

The effects of lowered cochlear temperature on eighth-nerve tuning were assessed by using forward masking of whole nerve action potential (AP) responses to generate AP tuning curves (APTCs) at cochlear temperatures ranging from 38.5 degrees to 30 degrees C for probe frequencies from 8 to 36 kHz. The data indicate that subnormal cochlear temperatures result in: broadened APTCs for probe frequencies above 10 kHz which are interpreted as resulting from reduced hair-cell frequency selectivity, lowered or more sensitive APTC tips where tone-burst thresholds are unchanged, and raised or less sensitive tips where thresholds to tone bursts were elevated. Increased tip sensitivity is explained in terms of enhanced eighth-nerve adaptation which occurred during hypothermia. Experiments directly addressing adaptation were performed, in which the masker-probe interval (delta t) was systematically lengthened. The normalized AP decrement versus delta t functions indicate an enhancement of both the amount and duration of adaptation during hypothermia. Functions relating the growth of response to the masker (AP decrement versus masker intensity functions) were reduced at low temperatures.     

Statistical measures of the power dropout ratio in semiconductor lasers subject to optical feedback

The influence of the optical feedback ratio and bias current on the mean and the standard deviation of the power dropout ratio of low-frequency fluctuations in external-cavity semiconductor lasers has been studied experimentally. The power dropout ratio was found to increase with increasing optical feedback ratio and to decrease with increasing bias current.     

Efficient population transfer by delayed pulses despite coupling ambiguity

In traditional schemes of multilevel multilaser excitation, each laser pulse interacts with only one pair of states, and the rotating wave approximation (RWA) is applicable. Here we study the population transfer process in a three-state system when each of the two lasers interacts with each of the pair of states and when the Rabi frequencies characterizing the interaction strengths of the system are comparable to or larger than the difference of the transition frequencies. We show that complete and robust population transfer is possible under conditions more general than those hitherto considered necessary for stimulated Raman adiabatic passage (STIRAP) or for successive π pulses. Using adiabatic Floquet theory we show that successful population transfer can be interpreted as adiabatic passage by means of a transfer state which connects the initial and final states. The Floquet picture offers a convenient interpretation of the population transfer as accompanied by multiple absorption of photons from or emission into the laser fields.     

An in vitro study of the use of photodynamic therapy for the treatment of natural oral plaque biofilms formed in vivo.

Seven-day oral plaque biofilms have been formed on natural enamel surfaces in vivo using a previously reported in situ device. The devices are then incubated with a cationic Zn(II) phthalocyanine photosensitizer and irradiated with white light. Confocal scanning laser microscopy (CSLM) of the biofilms shows that the photosensitizer is taken up into the biomass of the biofilm and that significant cell death is caused by photodynamic therapy (PDT). In addition, the treated biofilms are much thinner than the control samples and demonstrate a different structure from the control samples, with little evidence of channels and a less dense biomass. Transmission electron microscopy (TEM) of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT. These results clearly demonstrate the potential value of PDT in the management of oral biofilms.     

Propargyl Amine Synthesis Catalysed by Gold and Copper Thin Films by Using Microwave‐Assisted Continuous‐Flow Organic Synthesis (MACOS)

An effective multi‐component reaction (MCR) protocol has been developed for the construction of propargyl amines from aldehydes, amines and terminal alkynes by using microwave‐assisted continuous‐flow organic synthesis (MACOS). The process is catalysed by thin films of either copper or gold that achieve temperatures in excess of 900 °C when irradiated with low levels of microwave power. The process works equally well for premixed solutions of the three starting materials, or as three separate streams, which improves the combinatorial efficiency of the method. The process tolerates a wide variety of functional groups and heterocycles, and conversion over these diverse substrates ranges from 70–90 %.     

The limits of determinacy in second order arithmetic: consistency and complexity strength

We prove that determinacy for all Boolean combinations of \({F_{\sigma \delta }}\) (Π ₃ ⁰ ) sets implies the consistency of second-order arithmetic and more. Indeed, it is equivalent to the statement saying that for every set X and every number n, there exists a β-model of Π _n ¹ -comprehension containing X. We prove this result by providing a careful level-by-level analysis of determinacy at the finite level of the difference hierarchy on \({F_{\sigma \delta }}\) (Π ₃ ⁰ ) sets in terms of both reverse mathematics, complexity and consistency strength. We show that, for n ≥ 1, determinacy for sets at the nth level in this difference hierarchy lies strictly between (in the reverse mathematical sense of logical implication) the existence of β-models of Π _n+2 ¹ -comprehension containing any given set X, and the existence of β-models of Δ _n+2 ¹ -comprehension containing any given set X. Thus the nth of these determinacy axioms lies strictly between Π _n+2 ¹ -comprehension and Δ _n+2 ¹ -comprehension in terms of consistency strength. The major new technical result on which these proof theoretic ones are based is a complexity theoretic one. The nth determinacy axiom implies closure under the operation taking a set X to the least Σ _n+1 admissible containing X (for n = 1; this is due to Welch [9]).     

Ammonium octahydrotriborate (NH4B3H8): new synthesis, structure, and hydrolytic hydrogen release

A metathesis reaction between unsolvated NaB(3)H(8) and NH(4)Cl provides a simple and high-yield synthesis of NH(4)B(3)H(8). Structure determination through X-ray single crystal diffraction analysis reveals weak N-H(δ+)---H(δ-)-B interaction in NH(4)B(3)H(8) and strong N-H(δ+)---H(δ-)-B interaction in NH(4)B(3)H(8)·18-crown-6·THF adduct. Pyrolysis of NH(4)B(3)H(8) leads to the formation of hydrogen gas with appreciable amounts of other volatile boranes below 160 °C. Hydrolysis experiments show that upon addition of catalysts, NH(4)B(3)H(8) releases up to 7.5 materials wt % hydrogen.