摘要:

We have constructed a simple, all solid‐state, time‐correlated single photon counting device for collecting decay profiles of chromophores attached to DNA fragments moving through a capillary tube filled with a sieving gel under the influence of an applied electric field (capillary electrophoresis). The major components of the instrument consist of an actively pulsed GaAlAs diode laser (&lgr;excitation=780 nm; &tgr;p<200 ps; repetition rate=80 MHz; average power=5.0 mW), single photon avalanche diode (dark count rate <50 cps; quantum efficiency=65% at 800 nm) and a PC board containing a constant fraction discriminator, time‐to‐amplitude converter, and an analog‐to‐digital converter (maximum processing count rate=3×106cps). The instrument possessed a response function of approximately 275 ps (full width at half‐maximum), adequate for measuring fluorescence lifetimes in the subnanosecond regime. To demonstrate the utility and the sensitivity of the instrument, dynamic measurements of fluorescence lifetimes for near‐IR dye‐labeled DNA fragments were measured during capillary electrophoresis for the identification of the dye‐labeled nucleotide bases via temporal discrimination. The results indicated that in a two‐dye experiment, in which only two of the four constituent bases which comprise DNA were labeled with unique fluorescent probes, the characteristic lifetime of the probe could be used to readily identify the terminal nucleotide base. Decay profiles were constructed from roughly 17 500 photoelectrons accumulated over a 2 s counting interval at a loading level of approximately 6.2×10−21mol (3900 molecules) of DNA per electrophoretic band. The lifetimes of the two labeling dyes were determined to be 669 ps (±42 ps) and 528 ps (±68 ps). ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147302

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new universal cell for studies of phase transitions is proposed and its versatility demonstrated with an intact tomato seed as a sample under investigation. The temperature of the sensor head is regulated by computer controlled Peltier elements. The cell allows fully automated recording of temperature (from −35 to 70 °C) profiles. A diode laser (830 nm) was used to generate thermal waves in the sample to observe phase transitions. Pyroelectric materials such as a 9‐&mgr;m polyvinylidenefluoride foil and a LiTaO3single crystal were used as detectors. No influence was observed on the noise behavior of the pyroelectric sensors due to the Peltier elements. An important issue was the thermal isolation of the pyroelectric sensor with respect to the environment, i.e., the temperature of the housing had to be stabilized. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147303

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A practical low‐frequency one‐dimensional vibration isolation system has been developed exploiting a previously developed crossed wire suspension technique. A table is supported by two such suspensions so as to be stiff in 5° of freedom but with a very long period in one horizontal direction. The rotation of the suspended mass in the original system is eliminated and the transfer function at high frequencies is greatly improved. Periods of 10 s were achieved in experimental tests, giving isolation of 40 dB at 1 Hz and up to 60 dB at 10 Hz. The system is suitable for one‐dimensional optics experiments or as a base for further stages of vibration isolation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147304

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This work describes an improved CO2laser intracavity photoacoustic spectrometer. It can detect and measure small quantities of trace gases in air. The measured absorption sensitivity of 3.3×10−10cm−1corresponds to a mixture of 11 pptv (volume parts per trillion) of ethene in nitrogen. The sensitivity and reliability of the instrument were enhanced by reducing the level of background signals originating from optical and acoustical sources. The sensitivity reached is comparable with the best existing continuous measuring instruments while the background signal is two orders of magnitude smaller. The improvements are described in detail and a comparison to previous work is made. A first measurement demonstrates the suitability of the apparatus for biological applications. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147274

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A system for grabbing integrated video frames produced by a remote camera is described. As part of the pointed platform in a balloon‐borne experiment, we use a video charge‐coupled‐device camera to obtain wide field star images. To obtain images with a sufficient signal‐to‐noise ratio, integration times of up to 1 s are required. In applications where the frame grabber and camera are physically close to each other, timing the frame grabber trigger is straightforward; however, there are several advantages to locating the frame grabber not on the balloon payload. As a result commands issued simultaneously to the frame grabber on the ground and the camera on the balloon can be delayed relative to each other, resulting in failure to acquire an image. We have developed a system where, at the end of an integration, a tone is injected into the video field preceding the transmission of the integrated frame; the tone is used on the ground by a decoder circuit to control the frame grabber acquisition of the integrated frame. The system has operated successfully in the flight of a stratospheric balloon‐borne telescope. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147305

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe the design, operation, and performance of a high capacity, single stage,3He refrigerator optimized for balloon‐borne payloads. A temperature of ∼0.2 K is routinely maintained for more than seven days at ∼100 &mgr;W total heat load. Recycling can be completed in less than 12 h. A simple design avoids valves and explicit heat switches, resulting in simplified construction and improved performance. A numerical model characterizes the operating temperature of the system over a large range of conditions. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147275

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An apparatus was constructed for use in investigating bipolar induction phenomena, and related experiments were performed. A metal conductor was placed between a pair of bipolar magnets, and they were simultaneously rotated to induce a trapezoidal wave form ac voltage, whereas rotating the metal conductor alone caused a dc voltage to be induced. Rotation of the magnets alone caused a sinusoidal ac voltage to be induced. Drawing on their results, a new type of rotation detection sensor with an extremely simple construction was conceived, and its practical usefulness was confirmed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147267

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A simple, low‐cost lock‐in amplifier was described. This system has an autotracking bandpass filter which synchronizes its center frequency automatically with the reference frequency ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147268

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on a method to avoid common mode related interferences by means of a voltage controlled current source. Our technique is discussed for the case of experimental investigations involving very low signal levels, as encountered in the study of small metallic samples, at very low temperatures. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147269

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The handling,insitutreatment, and analysis of powdered samples under ultrahigh vacuum conditions can be quite difficult. New sample holder designs are presented which overcome most frequent problems associated with powders. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147270

出版商:AIP    

年代:1996

数据来源: AIP