We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which ...are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color–magnitude and color–color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a T(eff) value and judge sample completeness over bins of T(eff) and spectral type. Except for types ≥T8 and T(eff) < 600 K, our census is statistically complete to the 20 pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law (dN/dM ∝ M^(-α) with α = 0.6 ± 0.1. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200 K < T(eff) < 1350 K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs ≥Y0.5 and with T(eff) < 400 K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.
We fabricated Cu-doped TiNxOy thin film resistors by using atomic layer deposition, optical lithography, dry etching, Ti/Cu/Ti/Au e-beam evaporation and lift-off processes. The results of the ...measurements of the resistance temperature dependence, non-linearity, S-parameters at 0.01–26 GHz and details of the breakdown mechanism under high-voltage stress are reported. The devices’ sheet resistance is 220 ± 8 Ω/□ (480 ± 20 µΩ*cm); intrinsic resistance temperature coefficient (TCR) is ~400 ppm/°C in the T-range of 10–300 K; and S-parameters versus frequency are flat up to 2 GHz with maximum variation of 10% at 26 GHz. The resistors can sustain power and current densities up to ~5 kW*cm−2 and ~2 MA*cm−2, above which they switch to high-resistance state with the sheet resistance equal to ~200 kΩ/□ (~0.4 Ω*cm) caused by nitrogen and copper desorption from TiNxOy film. The Cu/Ti/TiNxOy contact is prone to ageing due to gradual titanium oxidation while the TiNxOy resistor body is stable. The resistors have strong potential for applications in high-frequency integrated and hybrid circuits that require small-footprint, medium-range resistors of 0.05–10 kΩ, with small TCR and high-power handling capability.
Abstract A complete accounting of nearby objects—from the highest-mass white dwarf progenitors down to low-mass brown dwarfs—is now possible, thanks to an almost complete set of trigonometric ...parallax determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census of objects within a Sun-centered sphere of 20 pc radius and check published literature to decompose each binary or higher-order system into its separate components. The result is a volume-limited census of ∼3600 individual star formation products useful in measuring the initial mass function across the stellar (<8 M ⊙ ) and substellar (≳5 M Jup ) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8 M ⊙ and a divergence at lower masses. Our 20 pc space densities are best fit with a quadripartite power law, ξ ( M ) = dN / dM ∝ M − α , with long-established values of α = 2.3 at high masses (0.55 < M < 8.00 M ⊙ ), and α = 1.3 at intermediate masses (0.22 < M < 0.55 M ⊙ ), but at lower masses, we find α = 0.25 for 0.05 < M < 0.22 M ⊙ , and α = 0.6 for 0.01 < M < 0.05 M ⊙ . This implies that the rate of production as a function of decreasing mass diminishes in the low-mass star/high-mass brown dwarf regime before increasing again in the low-mass brown dwarf regime. Correcting for completeness, we find a star to brown dwarf number ratio of, currently, 4:1, and an average mass per object of 0.41 M ⊙ .
Soliton microcombs constitute chip-scale optical frequency combs, and have the potential to impact a myriad of applications from frequency synthesis and telecommunications to astronomy. The ...demonstration of soliton formation via self-injection locking of the pump laser to the microresonator has significantly relaxed the requirement on the external driving lasers. Yet to date, the nonlinear dynamics of this process has not been fully understood. Here, we develop an original theoretical model of the laser self-injection locking to a nonlinear microresonator, i.e., nonlinear self-injection locking, and construct state-of-the-art hybrid integrated soliton microcombs with electronically detectable repetition rate of 30 GHz and 35 GHz, consisting of a DFB laser butt-coupled to a silicon nitride microresonator chip. We reveal that the microresonator's Kerr nonlinearity significantly modifies the laser diode behavior and the locking dynamics, forcing laser emission frequency to be red-detuned. A novel technique to study the soliton formation dynamics as well as the repetition rate evolution in real-time uncover non-trivial features of the soliton self-injection locking, including soliton generation at both directions of the diode current sweep. Our findings provide the guidelines to build electrically driven integrated microcomb devices that employ full control of the rich dynamics of laser self-injection locking, key for future deployment of microcombs for system applications.
A complete accounting of nearby objects -- from the highest-mass white dwarf
progenitors down to low-mass brown dwarfs -- is now possible, thanks to an
almost complete set of trigonometric parallax ...determinations from Gaia,
ground-based surveys, and Spitzer follow-up. We create a census of objects
within a Sun-centered sphere of 20-pc radius and check published literature to
decompose each binary or higher-order system into its separate components. The
result is a volume-limited census of $\sim$3,600 individual star formation
products useful in measuring the initial mass function across the stellar ($<8
M_\odot$) and substellar ($\gtrsim 5 M_{Jup}$) regimes. Comparing our resulting
initial mass function to previous measurements shows good agreement above
0.8$M_\odot$ and a divergence at lower masses. Our 20-pc space densities are
best fit with a quadripartite power law, $\xi(M) = dN/dM \propto M^{-\alpha}$
with long-established values of $\alpha = 2.3$ at high masses ($0.55 < M < 8.00
M_\odot$) and $\alpha = 1.3$ at intermediate masses ($0.22 < M < 0.55
M_\odot$), but at lower masses we find $\alpha = 0.25$ for $0.05 < M <0.22
M_\odot$ and $\alpha = 0.6$ for $0.01 < M < 0.05 M_\odot$. This implies that
the rate of production as a function of decreasing mass diminishes in the
low-mass star/high-mass brown dwarf regime before increasing again in the
low-mass brown dwarf regime. Correcting for completeness, we find a star to
brown dwarf number ratio of, currently, 4:1, and an average mass per object of
0.41 $M_\odot$.
We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which ...are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color-magnitude and color-color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a \(T_{\rm eff}\) value and judge sample completeness over bins of \(T_{\rm eff}\) and spectral type. Except for types \(\ge\) T8 and \(T_{\rm eff} <\) 600K, our census is statistically complete to the 20-pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law (\(dN/dM \propto M^{-\alpha}\)) with \(\alpha = 0.6{\pm}0.1\). We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200K \(< T_{\rm eff} <\) 1350K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs \(\ge\)Y0.5 and with \(T_{\rm eff} <\) 400K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.
A complete accounting of nearby objects -- from the highest-mass white dwarf progenitors down to low-mass brown dwarfs -- is now possible, thanks to an almost complete set of trigonometric parallax ...determinations from Gaia, ground-based surveys, and Spitzer follow-up. We create a census of objects within a Sun-centered sphere of 20-pc radius and check published literature to decompose each binary or higher-order system into its separate components. The result is a volume-limited census of \(\sim\)3,600 individual star formation products useful in measuring the initial mass function across the stellar (\(<8 M_\odot\)) and substellar (\(\gtrsim 5 M_{Jup}\)) regimes. Comparing our resulting initial mass function to previous measurements shows good agreement above 0.8\(M_\odot\) and a divergence at lower masses. Our 20-pc space densities are best fit with a quadripartite power law, \(\xi(M) = dN/dM \propto M^{-\alpha}\) with long-established values of \(\alpha = 2.3\) at high masses (\(0.55 < M < 8.00 M_\odot\)) and \(\alpha = 1.3\) at intermediate masses (\(0.22 < M < 0.55 M_\odot\)), but at lower masses we find \(\alpha = 0.25\) for \(0.05 < M <0.22 M_\odot\) and \(\alpha = 0.6\) for \(0.01 < M < 0.05 M_\odot\). This implies that the rate of production as a function of decreasing mass diminishes in the low-mass star/high-mass brown dwarf regime before increasing again in the low-mass brown dwarf regime. Correcting for completeness, we find a star to brown dwarf number ratio of, currently, 4:1, and an average mass per object of 0.41 \(M_\odot\).
Aim.
To evaluate the efficacy and safety of dexamethasone at various doses in an experimental model of direct acute lung injury (ALI).
Materials and methods.
The study was performed on 80 white ...outbred male rats, in which ALI was modeled by intratracheal administration of lipopolysaccharide. The animals were divided into 4 groups: the control group and three experimental groups (groups 1–3), where the animals were intraperitoneally administered dexamethasone at doses of 0.52, 1.71, and 8.00 mg / kg / day, respectively, for 3 days. A complete blood count, blood biochemistry test, and hemostatic tests were performed to assess the efficacy and safety of dexamethasone on day 3 of the experiment The severity of pulmonary edema was assessed by changes in the lung weight coefficient and the wet / dry weight ratio.
Results.
The use of dexamethasone in the ALI model increased the survival of rats in groups 1 and 2 by 35% (
p
< 0.05), and in group 3 only by 20% compared with control animals. The rat lung weight coefficient and the wet / dry weight ratio when using dexamethasone at all doses studied were equally reduced by an average of 28% (
p
< 0.05) and 17% (
p
< 0.05), respectively (
p
< 0.05). The severity of side effects of dexamethasone (hyperglycemia, hyperproteinemia, hyperkalemia, hypercoagulability, increased activity of creatine phosphokinase in the blood) was dose-dependent and was maximum in group 3 (dexamethasone dose 8.00 mg / kg / day).
Conclusion.
The effectiveness of both low (0.52 mg / kg / day) and high (8.00 mg / kg / day) doses of dexamethasone in an experimental model of ALI in rats is characterized by the same anti-edematous effect. Based on the results of the blood tests and the analysis of rat survival, the use of dexamethasone at the lowest dose (0.52 mg / kg / day) should be considered the safest.
The effects of short- and long-term administrations of dexamethasone on survival, severity of pulmonary edema, and hemostasis on experimental lipopolysaccharide-induced acute lung injury in rats were ...analyzed. Acute lung injury in rats was modeled by the intratracheal injection of lipopolysaccharide from the Salmonella enterica cell wall. White male rats were randomly divided into nine groups: the intact group consisted of 10 animals; two control groups of 20 animals each, in which acute lung injury was simulated without further treatment and removed from the experiment on day 3 or 7; six comparison groups of 20 animals each, in which, 3 h after modeling of acute lung injury and then once a day for 3 days (short mode of administration) or 7 days (long mode of administration), dexamethasone solution was administered intraperitoneally in the following doses: 0. 52 (equivalent to 6 mg/day for humans), 1. 71 (20 mg/day for humans), and 8 mg/kg/day (94 mg/day, pulse therapy for humans). On days 3 and 7, the survival rate, coagulogram values (active partial thromboplastin time, prothrombin time, activity of antithrombin, and soluble fibrin monomer complexes), and low-frequency piezotromboelastography data were assessed in the surviving animals. The results revealed that dexamethasone reduces mortality in acute lung injury and has a dose-dependent effect on the hemostasis system: with an increase in the dose administered, blood clotting processes increase and fibrinolysis is inhibited. Low-frequency piezothromboelastography with a conventional coagulogram allows for a comprehensive assessment of the hemostasis system, identifying violations, and timely drug correction.
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