26,644 research outputs found
Thermal Lensing Spectroscopy With Picosecond Pulse Trains and a New Dual Beam Configuration
In this communication, we wish to report on the use of synchronously mode-locked picosecond lasers in a pump-probe configuration for TL spectroscopy. The peak power for these picosecond lasers is very high and, of course, the fundamental of the dye laser (red beam) can be efficiently (~10%) doubled in frequency (U.V. beam) by second harmonic generation in nonlinear crystals. We use this generated U.V. beam as a probe to monitor the very weak absorption of the red beam. An arrangement [4] of the beams involving different waist positions for the pump and probe is used. This arrangement results in an enhancement of sensitivity (at least a factor of three to seven). Also, a different dependence of the signal on the cell position compared to the single beam method is obtained. Finally, we have obtained the Δν = 5 CH-stretching overtone absorption spectrum of liquid toluene with this method (see Figure 1). Suggestions are made regarding new applications of this picosecond pulse thermal lensing technique
Recycle, reduce, and reflect: information overload and knowledge deficit in the field of foreign investment and the law
’Eyes free’ in-car assistance: parent and child passenger collaboration during phone calls
This paper examines routine family car journeys, looking specifically at how passengers assist during a mobile telephone call while the drivers address the competing demands of handling the vehicle, interacting with various artefacts and controls in the cabin, and engage in co-located and remote conversations while navigating through busy city roads. Based on an analysis of video fragments, we see how drivers and child passengers form their conversations and requests around the call so as to be meaningful and paced to the demands, knowledge and abilities of their cooccupants, and how the conditions of the road and emergent traffic are oriented to and negotiated in the context of the social interaction that they exist alongside. The study provides implications for the design of car-based collaborative media and considers how hands- and eyesfree natural interfaces could be tailored to the complexity of activities in the car and on the road
ERS Farm Typology for a Diverse Agricultural Sector
The Economic Research Service (ERS) developed a farm typology which categorizes farms into more homogeneous groups than do classifications based on sales volume alone, producing a more effective policy development tool. The typology is used to describe U.S. farms.Farm Management,
Pesticide effects on body temperature of torpid/hibernating rodents (Peromyscus leucopus and Spermophilus tridecemlineatus)
Environmental contaminants have been shown in the lab to alter thyroid hormone concentrations. Despite the role these hormones play in the physiological ecology of small mammals, no one has investigated the possible
effects of thyroid-disrupting chemicals on mammalian thermal ecology and thermoregulatory ability. Because the energetic impact of such a disruption is likely to be most dramatic during times already energetically stressful, we investigated the effects of two common pesticides (atrazine and lindane) on the use of daily torpor in white-footed mice, and the use of hibernation in 13-lined ground squirrels. Fortunately, we found that these strategies for over-wintering success were not impaired
The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations
A microscopic theory for the NMR anomalies of the planar Cu and O sites in
superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains
the observations without the need to invoke anit-ferromagnetic spin
fluctuations on the planar Cu sites and its significant discrepancy with the
observed incommensurate neutron spin fluctuations. The theory is derived from
the recently published ab-initio band structure calculations that correct LDA
computations tendency to overestimate the self-coulomb repulsion for the
half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure
leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O
p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma
orbitals. This band structure is part of a new theory for the cuprates that
explains a broad range of experiments and is based upon the formation of Cooper
pairs comprised of a k up spin electron from one band and a -k down spin
electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also
http://www.firstprinciples.com. Minor changes to references and figure
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Direct picosecond time resolution of unimolecular reactions initiated by local mode excitation
The concept of local mode (LM) states [1] in large molecules raises the possibilty of inducing chemical reactions from a well-defined initial state (bond-selective chemistry). The results of linewidth and energy measurements in gases, [2(a)] and low temperature solids, [2(b)] however, indicate that the relaxation times for such high energy (> 15000 cm^-1) states can be extremely short, < 1ps. Because of the lack of direct time-resolved measurements, the following fundamental questions have not been unequivocally answered: What are the homogeneous linewidths of LM states and what are the rates of energy relaxation or reaction out of these states? Over the past five years we have made several attempts to observe the picosecond dynamics of LM states. Due to the inherent difficulties associated with making these measurements, such as the very small oscillator strength (σ < 10^-23 cm^2), an extremely sensitive probing technique becomes imperative
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