Darren Wong - Academia.edu (original) (raw)

Papers by Darren Wong

Research paper thumbnail of ANALYZING THE REDSHIFT CHARACTERISTICS OF AZULENIC, NAPHTHYL, OTHER RING-FUSED AND RETINYL PIGMENT ANALOGS OF BACTERIORHODOPSIN

Photochemistry and Photobiology, 1993

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR)... more Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (αRS): perturbation of the basic chromophore (SB shift, ΔSB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.

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Research paper thumbnail of The photoelectric effect: experimental confirmation concerning a widespread misconception in the theory

European Journal of Physics, 2011

The photoelectric effect is widely taught in schools and institutions. It is common knowledge tha... more The photoelectric effect is widely taught in schools and institutions. It is common knowledge that in order for photoelectrons to be emitted, the energy of the incoming photons must be greater than the work function of the irradiated metal (i.e. hν > phiemitter). However, what may not be as commonly known is that the 'phi' in Einstein's photoelectric equation (eVs = hν - phi) is often implicitly and mistakenly taken as the work function of the emitter (or anode) rather than that of the collector (or cathode). This paper provides experimental evidence for the more correct but the non-intuitive form of the photoelectric equation eVs = hν - phicollector, which can also be theoretically derived by taking into account the contact potential difference between the electrodes. This equation is shown experimentally to be invalid for hν < phiemitter and hν > phicollector, even though in such a case a positive Vs (stopping potential) is obtained by the equation, no Vs is obtainable experimentally. However, the equation is valid for hν < phicollector and hν > phiemitter where a negative Vs is obtained from the equation, which corresponds to an experimentally observed 'starting potential'.

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Research paper thumbnail of Correlation of Measured Soft X-Ray Pulses With Modeled Dynamics of the Plasma Focus

The six-phase Lee model code is used to fit the computed current waveform to the measured current... more The six-phase Lee model code is used to fit the computed current waveform to the measured current waveform of INTI plasma focus (PF; 2.2 kJ at 12 kV), a T2 PF device, operated as a source of neon soft X-ray (SXR) with optimum yield around 2 torr of neon. The characteristic He-like and H-like neon line SXR pulse is measured using a pair of SXR detectors with selected filters that, by subtraction, has a photon energy window of 900 to 1550 eV covering the region of the characteristic neon SXR lines. From the analysis of the fitted current and the measured SXR pulses, the characteristic neon SXR pulses are correlated to the pinch dynamics, and the subsequent slightly harder SXR pulses are correlated to the anomalous resistance phase. The characteristic neon SXR yield is measured; the pulse has a duration of 25 ns. The characteristic neon SXR typically starts 10 ns before the pinch phase and continues through the end of the 10-ns pinch phase, tailing into the anomalous resistance phase. Harder SXR pulses, probably Bremsstrahlung, are correlated to the anomalous resistance phase, with the main pulse occurring nearly 200 ns after the characteristic neon SXR pulse.

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Research paper thumbnail of A datalogger demonstration of electromagnetic induction with a falling, oscillating and swinging magnet

Physics Education, 2010

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Research paper thumbnail of New Microsoft Office Word Document

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Research paper thumbnail of ANALYZING THE REDSHIFT CHARACTERISTICS OF AZULENIC, NAPHTHYL, OTHER RING-FUSED AND RETINYL PIGMENT ANALOGS OF BACTERIORHODOPSIN

Photochemistry and Photobiology, 1993

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR)... more Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (αRS): perturbation of the basic chromophore (SB shift, ΔSB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.

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Research paper thumbnail of The photoelectric effect: experimental confirmation concerning a widespread misconception in the theory

European Journal of Physics, 2011

The photoelectric effect is widely taught in schools and institutions. It is common knowledge tha... more The photoelectric effect is widely taught in schools and institutions. It is common knowledge that in order for photoelectrons to be emitted, the energy of the incoming photons must be greater than the work function of the irradiated metal (i.e. hν > phiemitter). However, what may not be as commonly known is that the 'phi' in Einstein's photoelectric equation (eVs = hν - phi) is often implicitly and mistakenly taken as the work function of the emitter (or anode) rather than that of the collector (or cathode). This paper provides experimental evidence for the more correct but the non-intuitive form of the photoelectric equation eVs = hν - phicollector, which can also be theoretically derived by taking into account the contact potential difference between the electrodes. This equation is shown experimentally to be invalid for hν < phiemitter and hν > phicollector, even though in such a case a positive Vs (stopping potential) is obtained by the equation, no Vs is obtainable experimentally. However, the equation is valid for hν < phicollector and hν > phiemitter where a negative Vs is obtained from the equation, which corresponds to an experimentally observed 'starting potential'.

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Research paper thumbnail of Correlation of Measured Soft X-Ray Pulses With Modeled Dynamics of the Plasma Focus

The six-phase Lee model code is used to fit the computed current waveform to the measured current... more The six-phase Lee model code is used to fit the computed current waveform to the measured current waveform of INTI plasma focus (PF; 2.2 kJ at 12 kV), a T2 PF device, operated as a source of neon soft X-ray (SXR) with optimum yield around 2 torr of neon. The characteristic He-like and H-like neon line SXR pulse is measured using a pair of SXR detectors with selected filters that, by subtraction, has a photon energy window of 900 to 1550 eV covering the region of the characteristic neon SXR lines. From the analysis of the fitted current and the measured SXR pulses, the characteristic neon SXR pulses are correlated to the pinch dynamics, and the subsequent slightly harder SXR pulses are correlated to the anomalous resistance phase. The characteristic neon SXR yield is measured; the pulse has a duration of 25 ns. The characteristic neon SXR typically starts 10 ns before the pinch phase and continues through the end of the 10-ns pinch phase, tailing into the anomalous resistance phase. Harder SXR pulses, probably Bremsstrahlung, are correlated to the anomalous resistance phase, with the main pulse occurring nearly 200 ns after the characteristic neon SXR pulse.

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Research paper thumbnail of A datalogger demonstration of electromagnetic induction with a falling, oscillating and swinging magnet

Physics Education, 2010

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Research paper thumbnail of New Microsoft Office Word Document

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