Monolayer graphene bolometer as a sensitive far-IR detector

In this paper we give a detailed analysis of the expected sensitivity and operating conditions in the power detection mode of a hot-electron bolometer (HEB) made from a few {\mu}m$^2$ of monolayer graphene (MLG) flake which can be embedded into either a planar antenna or waveguide circuit via NbN (or NbTiN) superconducting contacts with critical temperature ~ 14 K. Recent data on the strength of the electron-phonon coupling are used in the present analysis and the contribution of the readout noise to the Noise Equivalent Power (NEP) is explicitly computed. The readout scheme utilizes Johnson Noise Thermometry (JNT) allowing for Frequency-Domain Multiplexing (FDM) using narrowband filter coupling of the HEBs. In general, the filter bandwidth and the summing amplifier noise have a significant effect on the overall system sensitivity. The analysis shows that the readout contribution can be reduced to that of the bolometer phonon noise if the detector device is operated at 0.05 K and the JNT signal is read at about 10 GHz where the Johnson noise emitted in equilibrium is substantially reduced. Beside the high sensitivity (NEP < 10$^{-20}$ W/Hz$^{1/2}$, this bolometer does not have any hard saturation limit and thus can be used for far-IR sky imaging with arbitrary contrast. By changing the operating temperature of the bolometer the sensitivity can be fine tuned to accommodate the background photon flux in a particular application. By using a broadband low-noise kinetic inductance parametric amplifier, ~100s of graphene HEBs can be read simultaneously without saturation of the system output.Comment: 9 pages. 6 figure, SPIE Astronomical Telescopes + Instrumentation, Montr\'eal, Quebec, Canada, 22-27 June, 201

Energy resolution of terahertz single-photon-sensitive bolometric detectors

We report measurements of the energy resolution of ultra-sensitive superconducting bolometric detectors. The device is a superconducting titanium nanobridge with niobium contacts. A fast microwave pulse is used to simulate a single higher-frequency photon, where the absorbed energy of the pulse is equal to the photon energy. This technique allows precise calibration of the input coupling and avoids problems with unwanted background photons. Present devices have an intrinsic full-width at half-maximum energy resolution of approximately 23 terahertz, near the predicted value due to intrinsic thermal fluctuation noise.Comment: 11 pages (double-spaced), 5 figures; minor revision

Decisions at the Brink: Locomotor Experience Affects Infants’ Use of Social Information on an Adjustable Drop-off

How do infants decide what to do at the brink of a precipice? Infants could use two sources of information to guide their actions: perceptual information generated by their own exploratory activity and social information offered by their caregivers. The current study investigated the role of locomotor experience in using social information—both encouragement and discouragement—for descending drop-offs. Mothers of 30 infants (experienced 12-month-old crawlers, novice 12-month-old walkers, and experienced 18-month-old walkers) encouraged and discouraged descent on a gradation of dropoffs (safe “steps” and risky “cliffs”). Novice walkers descended more frequently than experienced crawlers and walkers and fell while attempting to walk over impossibly high cliffs. All infants showed evidence of integrating perceptual and social information, but locomotor experience affected infants’ use of social messages, especially on risky dropoffs. Experienced crawlers and walkers selectively deferred to social information when perceptual information is ambiguous. In contrast, novice walkers took mothers’ advice inconsistently and only at extreme drop-offs

Small Black Holes on Branes: Is the horizon regular or singular ?

We investigate the following question: Consider a small mass, with $\epsilon$ (the ratio of the Schwarzschild radius and the bulk curvature length) much smaller than 1, that is confined to the TeV brane in the Randall-Sundrum I scenario. Does it form a black hole with a regular horizon, or a naked singularity? The metric is expanded in $\epsilon$ and the asymptotic form of the metric is given by the weak field approximation (linear in the mass). In first order of $\epsilon$ we show that the iteration of the weak field solution, which includes only integer powers of the mass, leads to a solution that has a singular horizon. We find a solution with a regular horizon but its asymptotic expansion in the mass also contains half integer powers.Comment: Accepted for publication in PR

The ties that bind: Cradling in Tajikistan

A traditional childrearing practice—“gahvora” cradling—in Tajikistan and other parts of Central Asia purportedly restricts movement of infants’ body and limbs. However, the practice has been documented only informally in anecdotal reports. Thus, this study had two research questions: (1) To what extent are infants’ movements restricted in the gahvora? (2) How is time in the gahvora distributed over a 24-hour day in infants from 1–24 months of age? To answer these questions, we video-recorded 146 mothers cradling their infants and interviewed them using 24-hour time diaries to determine the distribution of time infants spent in the gahvora within a day and across age. Infants’ movements were indeed severely restricted. Although mothers showed striking uniformity in how they restricted infants’ movements, they showed large individual differences in amount and distribution of daily use. Machine learning algorithms yielded three patterns of use: day and nighttime cradling, mostly nighttime cradling, and mostly daytime cradling, suggesting multiple functions of the cradling practice. Across age, time in the gahvora decreased, yet 20% of 12- to 24-montholds spent more than 15 hours bound in the gahvora. We discuss the challenges and benefits of cultural research, and how the discovery of new phenomena may defy Western assumptions about childrearing and development. Future work will determine whether the extent and timing of restriction impacts infants’ physical and psychological development