G. Ihas | University of Florida (original) (raw)
Papers by G. Ihas
Journal of Low Temperature Physics, 2004
SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1185 / INIST-CNRS ... more SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1185 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
ABSTRACT The conduction mechanisms and e!ect of magnetic "eld for Ge-"lm thermo... more ABSTRACT The conduction mechanisms and e!ect of magnetic "eld for Ge-"lm thermometers in the 25 mK to 4.2 K temperature range and magnetic "elds up to 6 T are studied. At low temperatures, the variable-range hopping conductivity prevails. At temperatures below 0.3 K, a gigantic negative magneto-resistance (up to 100%) is observed. The temperature dependence of resistance and magneto-resistance shows that localization behavior near the mobility edge exists. To explain experimental results, we adopt a phenomenological model based on variable-range hopping below the mobility edge. We also use a scaling theory of localization with a localization length depending on the mobility edge loca-tion. 2000 Published by Elsevier Science B.V. All rights reserved.
Physica B: Condensed Matter, 2000
Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=... more Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=3×106 to examine He I and He II turbulence in the presence of shear. The extremely low kinematic viscosity of liquid helium allows us to achieve high Reynolds numbers in small laboratory apparatus. Our results agree with those using classical fluids, showing the utility of
Journal of Fluid Mechanics, 2002
We demonstrate that an unusually small pipe flow apparatus using both liquid helium and room temp... more We demonstrate that an unusually small pipe flow apparatus using both liquid helium and room temperature gases can span an enormous range of Reynolds numbers. This paper describes the construction and operation of the apparatus in some detail. A wide range of Reynolds numbers is an advantage in any experiment seeking to establish scaling laws. This experiment also adds to evidence already in hand that the normal phase of liquid helium is a Navier–Stokes fluid. Finally, we explore recent questions concerning the influence of molecular motions on the transition to turbulence (Muriel 1998) and are unable to observe any influence.
Quantum Statistics and the Many-Body Problem, 1975
The first part of the paper concerns the experimental determination of the two-dimensional effect... more The first part of the paper concerns the experimental determination of the two-dimensional effective interaction potential between 3He atoms adsorbed on the surface of liquid 4He. Measurements of the velocity of surface sound and of the surface tension indicate that, for concentrations of 3He corresponding to a small fraction of a monolayer, the interaction is very weak and predominantly repulsive. This is unfavorable for a low-temperature super-fluid condensation.
Physical Review Letters, 1975
ABSTRACT
Applied Physics Letters, 2007
ABSTRACT Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resi... more ABSTRACT Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resistance thermometers, at temperatures below 0.2 K and magnetic fields below 1 T . This effect is very sensitive to temperature. At T≪0.3 K , the magnetoresistance is negative, and its magnitude increases with decreasing temperature. At 0.03 K , the resistance strongly decreases (up to 100 times) when the magnetic field is increased from 0 to 1 T and then saturates in higher fields. We discuss the mechanisms of this phenomenon and present results of calculations involving the hopping theory of conductivity with localization corrections.
3He has been increasing in both price and rarity, as well as its usage. Efficient recovery of 3He... more 3He has been increasing in both price and rarity, as well as its usage. Efficient recovery of 3He can be achieved with the use of a single-shot cryopump, or a dipstick. Simply connecting a dipstick filled with ac-tivated charcoal at liquid helium temperatures to a source of 3He, 62 cm3 of 3He can be collected for every cm3 of volume in the dipstick. Improving the design of the dipstick will increase the amount of 3He collected. I
Journal of Fluid Mechanics, 2002
Physica B-condensed Matter, 2000
Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=... more Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=3×106 to examine He I and He II turbulence in the presence of shear. The extremely low kinematic viscosity of liquid helium allows us to achieve high Reynolds numbers in small laboratory apparatus. Our results agree with those using classical fluids, showing the utility of helium as a fluid for turbulence research.
Journal of Low Temperature Physics, 2000
AIP Conference Proceedings, 1989
AIP Conference Proceedings, 1983
The authors have made phase-velocity change measurements for 5 and 15 MHz zero sound within a few... more The authors have made phase-velocity change measurements for 5 and 15 MHz zero sound within a few microkelvin of the ³He superfluid transition, T/sub c/, at 31.1 bar. The results show no marked feature at homega = 2..delta..(T). However, there is a marked reduction in the slope of dc/dT upon passing from the A-phase into the Al-phase. 2 references.
AIP Conference Proceedings, 1983
We report measurements of the temperature dependent far infrared (10-100 cm-1) reflectance and mi... more We report measurements of the temperature dependent far infrared (10-100 cm-1) reflectance and milliKelvin transport of highly conducting polyaniline doped with d,1-camphorsulfonic acid (PAN-CSA) and polypyrrole doped with hexafluorophosphate (PPy-PF_6). With decreasing T (to ~ 200 K), the reflectance initially increases for omega > 20 cm-1 and decreases at lower frequencies. As T is further decreased, there is a continuous
Journal of Low Temperature Physics, 2004
SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1185 / INIST-CNRS ... more SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1185 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
ABSTRACT The conduction mechanisms and e!ect of magnetic "eld for Ge-"lm thermo... more ABSTRACT The conduction mechanisms and e!ect of magnetic "eld for Ge-"lm thermometers in the 25 mK to 4.2 K temperature range and magnetic "elds up to 6 T are studied. At low temperatures, the variable-range hopping conductivity prevails. At temperatures below 0.3 K, a gigantic negative magneto-resistance (up to 100%) is observed. The temperature dependence of resistance and magneto-resistance shows that localization behavior near the mobility edge exists. To explain experimental results, we adopt a phenomenological model based on variable-range hopping below the mobility edge. We also use a scaling theory of localization with a localization length depending on the mobility edge loca-tion. 2000 Published by Elsevier Science B.V. All rights reserved.
Physica B: Condensed Matter, 2000
Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=... more Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=3×106 to examine He I and He II turbulence in the presence of shear. The extremely low kinematic viscosity of liquid helium allows us to achieve high Reynolds numbers in small laboratory apparatus. Our results agree with those using classical fluids, showing the utility of
Journal of Fluid Mechanics, 2002
We demonstrate that an unusually small pipe flow apparatus using both liquid helium and room temp... more We demonstrate that an unusually small pipe flow apparatus using both liquid helium and room temperature gases can span an enormous range of Reynolds numbers. This paper describes the construction and operation of the apparatus in some detail. A wide range of Reynolds numbers is an advantage in any experiment seeking to establish scaling laws. This experiment also adds to evidence already in hand that the normal phase of liquid helium is a Navier–Stokes fluid. Finally, we explore recent questions concerning the influence of molecular motions on the transition to turbulence (Muriel 1998) and are unable to observe any influence.
Quantum Statistics and the Many-Body Problem, 1975
The first part of the paper concerns the experimental determination of the two-dimensional effect... more The first part of the paper concerns the experimental determination of the two-dimensional effective interaction potential between 3He atoms adsorbed on the surface of liquid 4He. Measurements of the velocity of surface sound and of the surface tension indicate that, for concentrations of 3He corresponding to a small fraction of a monolayer, the interaction is very weak and predominantly repulsive. This is unfavorable for a low-temperature super-fluid condensation.
Physical Review Letters, 1975
ABSTRACT
Applied Physics Letters, 2007
ABSTRACT Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resi... more ABSTRACT Large negative magnetoresistance is found in Ge films, used as ultralow-temperature resistance thermometers, at temperatures below 0.2 K and magnetic fields below 1 T . This effect is very sensitive to temperature. At T≪0.3 K , the magnetoresistance is negative, and its magnitude increases with decreasing temperature. At 0.03 K , the resistance strongly decreases (up to 100 times) when the magnetic field is increased from 0 to 1 T and then saturates in higher fields. We discuss the mechanisms of this phenomenon and present results of calculations involving the hopping theory of conductivity with localization corrections.
3He has been increasing in both price and rarity, as well as its usage. Efficient recovery of 3He... more 3He has been increasing in both price and rarity, as well as its usage. Efficient recovery of 3He can be achieved with the use of a single-shot cryopump, or a dipstick. Simply connecting a dipstick filled with ac-tivated charcoal at liquid helium temperatures to a source of 3He, 62 cm3 of 3He can be collected for every cm3 of volume in the dipstick. Improving the design of the dipstick will increase the amount of 3He collected. I
Journal of Fluid Mechanics, 2002
Physica B-condensed Matter, 2000
Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=... more Turbulent pipe flow of liquid 4He has been investigated for Reynolds numbers from Re=3×103 to Re=3×106 to examine He I and He II turbulence in the presence of shear. The extremely low kinematic viscosity of liquid helium allows us to achieve high Reynolds numbers in small laboratory apparatus. Our results agree with those using classical fluids, showing the utility of helium as a fluid for turbulence research.
Journal of Low Temperature Physics, 2000
AIP Conference Proceedings, 1989
AIP Conference Proceedings, 1983
The authors have made phase-velocity change measurements for 5 and 15 MHz zero sound within a few... more The authors have made phase-velocity change measurements for 5 and 15 MHz zero sound within a few microkelvin of the ³He superfluid transition, T/sub c/, at 31.1 bar. The results show no marked feature at homega = 2..delta..(T). However, there is a marked reduction in the slope of dc/dT upon passing from the A-phase into the Al-phase. 2 references.
AIP Conference Proceedings, 1983
We report measurements of the temperature dependent far infrared (10-100 cm-1) reflectance and mi... more We report measurements of the temperature dependent far infrared (10-100 cm-1) reflectance and milliKelvin transport of highly conducting polyaniline doped with d,1-camphorsulfonic acid (PAN-CSA) and polypyrrole doped with hexafluorophosphate (PPy-PF_6). With decreasing T (to ~ 200 K), the reflectance initially increases for omega > 20 cm-1 and decreases at lower frequencies. As T is further decreased, there is a continuous