Terahertz emission from the intrinsic Josephson junctions of high-symmetry thermally-managed Bi2Sr2CaCu2O8+δ microstrip antennas

We show for high-symmetry disk, square, or equilateral triangular thin microstrip antennas of any composition respectively obeying C∞v, C4v, and C3v point group symmetries, that the transverse magnetic electromagnetic cavity mode wave functions are restricted in form to those that are one-dimensional representations of those point groups. Plots of the common nodal points of the ten lowest-energy non-radiating two-dimensional representations of each of these three symmetries are presented. For comparison with symmetry-broken disk intrinsic Josephson junction microstrip antennas constructed from the highly anisotropic layered superconductor Bi2 Sr2 CaCu2 O8+δ (BSCCO), we present plots of the ten lowest frequency orthonormal wave functions and of their emission power angular distributions. These results are compared with previous results for square and equilateral triangular thin microstrip antennas

The use of adherence aids by adults with diabetes: A cross-sectional survey

BACKGROUND: Adherence with medication taking is a major barrier to physiologic control in diabetes and many strategies for improving adherence are in use. We sought to describe the use of mnemonic devices and other adherence aids by adults with diabetes and to investigate their association with control of hyperglycemia, hyperlipidemia and hypertension. METHODS: Cross sectional survey of diabetic adults randomly selected from Primary Care practices in the Vermont Diabetes Information System. We used linear regression to examine the associations between the use of various aids and physiologic control among subjects who used oral agents for hyperglycemia, hypercholesterolemia, and hypertension. RESULTS: 289 subjects (mean age 65.4 years; 51% female) used medications for all three conditions. Adherence aids were reported by 80%. The most popular were day-of-the-week pill boxes (50%), putting the pills in a special place (41%), and associating pill taking with a daily event such as a meal, TV show, or bedtime (11%). After adjusting for age, sex, marital status, income, and education, those who used a special place had better glycemic control (A1C -0.36%; P = .04) and systolic blood pressure (-5.9 mm Hg; P = .05) than those who used no aids. Those who used a daily event had better A1C (-0.56%; P = .01) than patients who used no aids. CONCLUSION: Although adherence aids are in common use among adults with diabetes, there is little evidence that they are efficacious. In this study, we found a few statistically significant associations with adherence aids and better diabetes control. However, these findings could be attributed to multiple comparisons or unmeasured confounders. Until more rigorous evaluations are available, it seems reasonable to recommend keeping medicines in a special place for diabetic adults prescribed multiple medications

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-Tcsuperconductor Bi2Sr2CaCu2O8 +δ

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting C3v point group symmetry. When the C3v operations are imposed upon the antenna, the TM(m,n) modes with wave vectors $\propto \sqrt{{{m}^{2}}+nm+{{n}^{2}}}$ are much less dense than commonly thought. The R3 operations restrict the integral n and m to satisfy $|m-n|\,=3p$ , where $p\geqslant 0$ and $p\geqslant 1$ for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature Tc superconductor Bi2Sr2CaCu2${{\text{O}}_{8+\delta}}$ , and fit the emissions data from an earlier sample for which the C3v symmetry was apparently broken

Cavity Mode Enhancement Of Terahertz Emission From Equilateral Triangular Microstrip Antennas Of The High-T C Superconductor Bi2Sr2Cacu2O8 + Δ

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting C 3v point group symmetry. When the C 3v operations are imposed upon the antenna, the TM(m,n) modes with wave vectors ∝√m2+nm+n2 are much less dense than commonly thought. The R3 operations restrict the integral n and m to satisfy |m-n|=3p, where p ≥ 0 and p ≥ 1 for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature T c superconductor Bi2Sr2CaCu2O8+δ, and fit the emissions data from an earlier sample for which the C 3v symmetry was apparently broken

Characterization of cavity mode and radiation pattern in superconducting coherent terahertz emitters

We discuss the broadly tunable terahertz (THz) radiation in solid state terahertz (THz) emitters based on high-temperature superconducting Bi2Sr2CaCu2O8+δ (Bi-2212). We experimentally measure the current-voltage characteristics (IVC) of mesas of different geometries, such as triangular-, pentagonal-, hexagonal-, and elliptical- cavities, and compare the IVC of the radiating and no-radiating cavities. The THz emission spectra in radiating THz cavities was measured using the Fourier transform infrared spectrometer in order to elucidate the radiation mechanism of the emitters. Moreover, we experimentally and theoretically study the angular dependence of the emission intensity obtained in mesas’ plane at various frequencies and detection angles, by rotating the sample holder relative to the detector, to identify the excited EM cavity modes within the cavities that participate in the emitter output power enhancement. Reference: [1] DP Cerkoney et al., J. Phys. Condens. Matter 29, 015601 (2016), [2] K. Delfanazari et al, J. Infrared Millim. Terahertz Waves 35, 131-146 (2014), [3] K. Delfanazari et al., IEEE Trans. Terahertz Sci. Technol. 5, 505-511 (2015), [4] K. Delfanazari et al., Opt. Express 21, 2171-2184 (2013)

(Invited) Emission distributivities from novel geometrical antennas

We model the angular distributions of the emissions from the transverse magnetic cavity modes of two types of antenna shapes. The six degenerate fundamental cavity excitations of a thin equilateral triangular antenna are studied using the magnetic Love equivalence principle [1,2,3], and used to fit the angular distributions of the emissions observed in two planes from such antennas consisting of mesas fabricated from the high-temperature superconductor Bi2Sr2CaCu2O8+Ⴅ (Bi2212) [2,3]. Similar fits are obtained for the dual-plane emissions detected from a thin acute isosceles triangular mesa antenna [4], which we model as a narrow-angle pie-shaped wedge antenna. The predictions for the TM(2,0)o cavity mode are found to be in good agreement with experiment [4] . Then we study the many predicted TM cavity modes present in thin pie-shaped wedge antennas of various wedge angles. Three-dimensional plots of some of the predicted angular distributions of the emissions from a variety of modes in a variety of pie-shaped wedge cavities are presented. References [1] R. A. Klemm and K. Kadowaki, J. Phys.: Condens. Matter 21, 375701 (2010). [2] R. A. Klemm et al., Physica C 491, 30 (2013). [3] K. Delfanazari et al., Physica C 491, 16 (2013). [4] K. Delfanazari et al., Opt. Express 21, 2171 (2013)

Terahertz emission from pie-shaped wedge microstrip antennas of the high-Tc superconductor Bi2Sr2CaCu2O8+δ

We calculate the standing wave functions for pie-shaped wedge microstrip antennas of various wedge angles ϕ0. We then calculate the emission distributions from the uniform Josephson current and from the excitation of a cavity mode generated from the stand wave functions. For a narrow dieter's pie slice, quantitative fits to the experimental data on a Bi2Sr2CaCu2O8+δ narrow isosceles triangular mesa are shown

(Invited) Cavity mode enhancement of terahertz emission from equilateral triangular and pieshaped wedge microstrip antennas of the high-temperature superconductor Bi2Sr2CaCu2O8+δ

We study the transverse magnetic (TM) electromagnetic cavity modes wave functions for ideal equilateral triangular and pie-shaped wedge microstrip antennas (MSAs), assuming perfect thermal management and perfect shape construction, such as could possibly be produced with improved versions of “stand-alone mesa sandwich structures” [1]. We use the two-source model for the emissions [2], the uniform Josephson current source and the magnetic surface current source driven by the displacement current. For perfect equilateral triangular MSAs obeying C3v point group symmetry, most cavity modes vanish, and both contributions to the output power from the non-vanishing cavity modes have angular dependencies obeying C6 symmetry. The power distribution from an earlier (conventional mesa) sample with emissions having lower symmetry are fit by assuming the C3v wave function symmetry is broken by a hot spot, yielding one or more of the symmetry-forbidden TM(1,0) modes [3]. Wedge MSAs with only one mirror plane have output power distributions obeying C2 symmetry. The wave functions and two-source power distributions from wedge MSAs with a variety of wedge angles φ0 are calculated, and the emissions from the TMo(2,0) mode are fit with the two-source model [3]. In both cases of fitting to the emissions from earlier conventional mesa form of MSAs, the superconducting substrate was treated as a perfect magnetic conductor, which was necessary due to its poor thermal conductivity [2]. References [1] T. Kashiwagi et al., Phys. Rev. Applied 4, 054018 (2015). [2] R. A. Klemm and K. Kadowaki, J. Phys.: Condens. Matter 22, 375701 (2010). [3] K. Delfanazari et al., Opt. Express 21, 2171 (2013)

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-Tc superconductor Bi2Sr2CaCu2O8+δ

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna exhibiting C3v point group symmetry, which restricts the number of TM(n,m) modes to |m−n|=3p, where the integer p>0 for the modes odd and even about the three mirror planes, but p=0 can also exist for the even modes. We calculate the wave functions and the power distribution forms from the uniform Josephson current source and from the excitation of one of these cavity modes, and fit data on an early equilateral triangular Bi2Sr2CaCu2O8+δ mesa, for which the C3v symmetry was apparently broken

(Invited) Terahertz emission from the intrinsic Josephson junctions of high-symmetry thermally-managed BSCCO microstrip antennas

We study the coherent terahertz emission from the intrinsic Josephson junctions in thermally-managed, high-symmetry, thin microstrip antennas constructed from single crystals of the highly two-dimensional, layered high-temperature superconductor BSCCO. The thin antennas studied are disk [1,2], square [3], and equilateral triangular [4,5] in shape. Upon application of a dc voltage across the junctions, the primary radiation source is the uniform ac Josephson current, but when the appropriate point in the current-voltage characteristics is found, the excitation of an electromagnetic cavity mode can lead to a considerable enhancement of the output power. When properly thermally managed by covering the top and bottom of a thin BSCCO crystallite with Au and sandwiching that between sapphire plates[6], only the one-dimensional representation wave functions of the appropriate point groups are excited, and the world record 2.4 THz emission from a superconductor was recently observed [2] from such a device. The coherent emission is widely tunable and has a narrow linewidth. The angular distributions of the output power are calculated and compared with experiment. [1] M. Tsujimoto et al., Phys. Rev. Lett. 105, 037005 (2010). [2] T. Kashiwagi et al., Appl. Phys. Lett. 107, 082601 (2015). [3] R. A. Klemm et al., IEEE JSTQE (2017, in press). [4] D. P. Cerkoney et al., J. Phys.: Condens. Matter 29, 015601 (2017). [5] K. Delfanazari et al., Opt. Express 21, 2171 (2013). [6] T. Kashiwagi et al., Phys. Rev. Applied 4, 054018 (2015)