100 research outputs found
Vector Reflectometry in a Beam Waveguide
We present a one-port calibration technique for characterization of beam
waveguide components with a vector network analyzer. This technique involves
using a set of known delays to separate the responses of the instrument and the
device under test. We demonstrate this technique by measuring the reflected
performance of a millimeter-wave variable-delay polarization modulator
Variable-delay Polarization Modulators for Cryogenic Millimeter-wave Applications
We describe the design, construction, and initial validation of the
variable-delay polarization modulator (VPM) designed for the PIPER cosmic
microwave background polarimeter. The VPM modulates between linear and circular
polarization by introducing a variable phase delay between orthogonal linear
polarizations. Each VPM has a diameter of 39 cm and is engineered to operate in
a cryogenic environment (1.5 K). We describe the mechanical design and
performance of the kinematic double-blade flexure and drive mechanism along
with the construction of the high precision wire grid polarizers.Comment: 8 pages, 10 Figures, Submitted to Review of Scientific Instrument
The Cosmology Large Angular Scale Surveyor (CLASS): 40 GHz Optical Design
The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19 deg x 14 deg with a resolution for each beam on the sky of 1.5 deg. FWHM
Normal perception of Mooney faces in developmental prosopagnosia: evidence from the N170 component and rapid neural adaptation
Individuals with developmental prosopagnosia (DP) have a severe difficulty recognizing the faces of known individuals in the absence of any history of neurological damage. These recognition problems may be linked to selective deficits in the holistic/configural processing of faces. We used two-tone Mooney images to study the processing of faces versus non-face objects in DP when it is based on holistic information (or the facial gestalt) in the absence of obvious local cues about facial features. A rapid adaptation procedure was employed for a group of 16 DPs. Naturalistic photographs of upright faces were preceded by upright or inverted Mooney faces or by Mooney houses. DPs showed face-sensitive N170 components in response to Mooney faces versus houses, and N170 amplitude reductions for inverted as compared to upright Mooney faces. They also showed the typical pattern of N170 adaptation effects, with reduced N170 components when upright naturalistic test faces were preceded by upright Mooney faces, demonstrating that the perception of Mooney and naturalistic faces recruits shared neural populations. Our findings demonstrate that individuals with DP can utilize global information about face configurations for categorical discriminations between faces and non-face objects, and suggest that face processing deficits emerge primarily at more fine-grained higher level stages of face perception
AutoML in the Age of Large Language Models: Current Challenges, Future Opportunities and Risks
The fields of both Natural Language Processing (NLP) and Automated Machine
Learning (AutoML) have achieved remarkable results over the past years. In NLP,
especially Large Language Models (LLMs) have experienced a rapid series of
breakthroughs very recently. We envision that the two fields can radically push
the boundaries of each other through tight integration. To showcase this
vision, we explore the potential of a symbiotic relationship between AutoML and
LLMs, shedding light on how they can benefit each other. In particular, we
investigate both the opportunities to enhance AutoML approaches with LLMs from
different perspectives and the challenges of leveraging AutoML to further
improve LLMs. To this end, we survey existing work, and we critically assess
risks. We strongly believe that the integration of the two fields has the
potential to disrupt both fields, NLP and AutoML. By highlighting conceivable
synergies, but also risks, we aim to foster further exploration at the
intersection of AutoML and LLMs
Perceptual face processing in developmental prosopagnosia is not sensitive to the canonical location of face parts
Individuals with developmental prosopagnosia (DP) are strongly impaired in recognizing faces, but it is controversial whether this deficit is linked to atypical visual-perceptual face processing mechanisms. Previous behavioural studies have suggested that face perception in DP might be less sensitive to the canonical spatial configuration of face parts in upright faces. To test this prediction, we recorded event-related brain potentials (ERPs) to intact upright faces and to faces with spatially scrambled parts (eyes, nose, and mouth) in a group of ten participants with DP and a group of ten age-matched control participants with normal face recognition abilities. The face-sensitive N170 component and the vertex positive potential (VPP) were both enhanced and delayed for scrambled as compared to intact faces in the control group. In contrast, N170 and VPP amplitude enhancements to scrambled faces were absent in the DP group. For control participants, the N170 to scrambled faces was also sensitive to feature locations, with larger and delayed N170 components contralateral to the side where all features appeared in a non-canonical position. No such differences were present in the DP group. These findings suggest that spatial templates of the prototypical feature locations within an upright face are selectively impaired in DP
The Primordial Inflation Polarization Explorer (PIPER)
The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne
cosmic microwave background (CMB) polarimeter designed to search for evidence
of inflation by measuring the large-angular scale CMB polarization signal.
BICEP2 recently reported a detection of B-mode power corresponding to the
tensor-to-scalar ratio r = 0.2 on ~2 degree scales. If the BICEP2 signal is
caused by inflationary gravitational waves (IGWs), then there should be a
corresponding increase in B-mode power on angular scales larger than 18
degrees. PIPER is currently the only suborbital instrument capable of fully
testing and extending the BICEP2 results by measuring the B-mode power spectrum
on angular scales = ~0.6 deg to 90 deg, covering both the reionization
bump and recombination peak, with sensitivity to measure the tensor-to-scalar
ratio down to r = 0.007, and four frequency bands to distinguish foregrounds.
PIPER will accomplish this by mapping 85% of the sky in four frequency bands
(200, 270, 350, 600 GHz) over a series of 8 conventional balloon flights from
the northern and southern hemispheres. The instrument has background-limited
sensitivity provided by fully cryogenic (1.5 K) optics focusing the sky signal
onto four 32x40-pixel arrays of time-domain multiplexed Transition-Edge Sensor
(TES) bolometers held at 140 mK. Polarization sensitivity and systematic
control are provided by front-end Variable-delay Polarization Modulators
(VPMs), which rapidly modulate only the polarized sky signal at 3 Hz and allow
PIPER to instantaneously measure the full Stokes vector (I, Q, U, V) for each
pointing. We describe the PIPER instrument and progress towards its first
flight.Comment: 11 pages, 7 figures. To be published in Proceedings of SPIE Volume
9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014,
conference 915
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