694 research outputs found
Neural mechanisms of visual singleton detection: Evidence from human electrophysiology
It is sometimes necessary to search for visual objects of potential interest that are underspecified (e.g., any illegal item in a suitcase). The search for such an object can be accomplished easily if it possesses a unique feature that makes it stand out from its surrounding. In this case, observers can simply search for the most salient item in the environment (singleton detection). Surprisingly, the neuro-cognitive processes involved in singleton detection are still poorly understood. The overarching aims of this thesis were to reveal neuro-cognitive processes involved in singleton detection using event-related potentials (ERPs) and to address specific questions about the role of attention in singleton-detection tasks. Experiment 1 reexamined the claim that attentional processes associated with an ERP component called the N2pc are absent in singleton detection. The results revealed several ERP components, including the N2pc and a newly discovered component that tracked the time course of singleton detection (the singleton detection positivity; SDP). It was concluded that singleton detection involves some of the same attentional processes as those required for feature-based search. Experiment 2 employed a go/no-go variant of the singleton-detection task to determine whether the attentional processes observed in singleton detection are triggered automatically, as some researchers believe. ERP indices of singleton detection (SDP) and attentional selection (N2pc) were markedly reduced or absent on no-go trials, demonstrating that rapid assessment of task relevancy can prevent salience-driven capture of attention in the singleton-detection task
The Future of Generic Biologics: Should the United States “Follow-On” the European Pathway?
The United States is embarking on a biotechnology drug revolution. In the last few decades, biotech drugs have saved millions of lives, and the market for these miracle cures continues to grow at an astronomical rate. Unfortunately, as the market for biotech drugs is skyrocketing, drug prices are following suit. As Congress strives to make these new drugs more affordable, it must not ignore significant safety concerns unique to these revolutionary therapies. Congress should follow the lead of the European Union to create an accessible pathway for generic forms of biotech drugs that includes strict regulatory measures to ensure drug safety and efficacy
Results at 24 months from the prospective, randomized, multicenter Investigational Device Exemption trial of ProDisc-C versus anterior cervical discectomy and fusion with 4-year follow-up and continued access patients.
BackgroundCervical total disk replacement (TDR) is intended to address pain and preserve motion between vertebral bodies in patients with symptomatic cervical disk disease. Two-year follow-up for the ProDisc-C (Synthes USA Products, LLC, West Chester, Pennsylvania) TDR clinical trial showed non-inferiority versus anterior cervical discectomy and fusion (ACDF), showing superiority in many clinical outcomes. We present the 4-year interim follow-up results.MethodsPatients were randomized (1:1) to ProDisc-C (PDC-R) or ACDF. Patients were assessed preoperatively, and postoperatively at 6 weeks and 3, 6, 12, 18, 24, 36, and 48 months. After the randomized portion, continued access (CA) patients also underwent ProDisc-C implantation, with follow-up visits up to 24 months. Evaluations included Neck Disability Index (NDI), Visual Analog Scale (VAS) for pain/satisfaction, and radiographic and physical/neurologic examinations.ResultsRandomized patients (103 PDC-R and 106 ACDF) and 136 CA patients were treated at 13 sites. VAS pain and NDI score improvements from baseline were significant for all patients (P < .0001) but did not differ among groups. VAS satisfaction was higher at all time points for PDC-R versus ACDF patients (P = .0499 at 48 months). The percentage of patients who responded yes to surgery again was 85.6% at 24 months and 88.9% at 48 months in the PDC-R group, 80.9% at 24 months and 81.0% at 48 months in the ACDF group, and 86.3% at 24 months in the CA group. Five PDC-R patients (48 months) and no CA patients (24 months) had index-level bridging bone. By 48 months, approximately 4-fold more ACDF patients required secondary surgery (3 of 103 PDC-R patients [2.9%] vs 12 of 106 ACDF patients [11.3%], P = .0292). Of these, 6 ACDF patients (5.6%) required procedures at adjacent levels. Three CA patients required secondary procedures (24 months).ConclusionsOur 4-year data support that ProDisc-C TDR and ACDF are viable surgical options for symptomatic cervical disk disease. Although ACDF patients may be at higher risk for additional surgical intervention, patients in both groups show good clinical results at longer-term follow-up
Surface Versus Bulk Dirac States Tuning in a Three-Dimensional Topological Dirac Semimetal
Recently, crystalline-symmetry-protected three-dimensional (3D) bulk Dirac
semimetal phase has been experimentally identified in a stoichiometric
high-mobility compound, Cd3As2. The Dirac state observed in Cd3As2 has been
attributed to originate mostly from the bulk state while calculations show that
the bulk and surface states overlap over the entire Dirac dispersion energy
range. In this study, we unambiguously reveal doping induced evolution of the
ground state of surface and bulk electron dynamics in a 3D Dirac semimetal. We
develop a systematic technique to isolate the surface and bulk states in
Cd3As2, by simultaneously utilizing angle-resolved photoemission spectroscopy
(ARPES) and in-situ surface deposition. Our experimental results provide a
method for tuning the chemical potential as well as to observe surface states
degenerate with bulk states, which will be useful for future applications of 3D
Dirac semimetal.Comment: 5 pages, 4 figure
Type-II Topological Dirac Semimetals: Theory and Materials Prediction (VAl3 family)
The discoveries of Dirac and Weyl semimetal states in spin-orbit compounds
led to the realizations of elementary particle analogs in table-top
experiments. In this paper, we propose the concept of a three-dimensional
type-II Dirac fermion and identify a new topological semimetal state in the
large family of transition-metal icosagenides, MA3 (M=V, Nb, Ta; A=Al, Ga, In).
We show that the VAl3 family features a pair of strongly Lorentz-violating
type-II Dirac nodes and that each Dirac node consists of four type-II Weyl
nodes with chiral charge +/-1 via symmetry breaking. Furthermore, we predict
the Landau level spectrum arising from the type-II Dirac fermions in VAl3 that
is distinct from that of known Dirac semimetals. We also show a topological
phase transition from a type-II Dirac semimetal to a quadratic Weyl semimetal
or a topological crystalline insulator via crystalline distortions. The new
type-II Dirac fermions, their novel magneto-transport response, the topological
tunability and the large number of compounds make VAl3 an exciting platform to
explore the wide-ranging topological phenomena associated with
Lorentz-violating Dirac fermions in electrical and optical transport,
spectroscopic and device-based experiments.Comment: 28 pages, 7 Figure
New fermions on the line in topological symmorphic metals
Topological metals and semimetals (TMs) have recently drawn significant
interest. These materials give rise to condensed matter realizations of many
important concepts in high-energy physics, leading to wide-ranging protected
properties in transport and spectroscopic experiments. The most studied TMs,
i.e., Weyl and Dirac semimetals, feature quasiparticles that are direct
analogues of the textbook elementary particles. Moreover, the TMs known so far
can be characterized based on the dimensionality of the band crossing. While
Weyl and Dirac semimetals feature zero-dimensional points, the band crossing of
nodal-line semimetals forms a one-dimensional closed loop. In this paper, we
identify a TM which breaks the above paradigms. Firstly, the TM features
triply-degenerate band crossing in a symmorphic lattice, hence realizing
emergent fermionic quasiparticles not present in quantum field theory.
Secondly, the band crossing is neither 0D nor 1D. Instead, it consists of two
isolated triply-degenerate nodes interconnected by multi-segments of lines with
two-fold degeneracy. We present materials candidates. We further show that
triplydegenerate band crossings in symmorphic crystals give rise to a Landau
level spectrum distinct from the known TMs, suggesting novel magneto-transport
responses. Our results open the door for realizing new topological phenomena
and fermions including transport anomalies and spectroscopic responses in
metallic crystals with nontrivial topology beyond the Weyl/Dirac paradigm.Comment: 24 pages, 4 figures, and 1 tabl
Atomic-scale visualization of quasiparticle interference on a type-II Weyl semimetal surface
We combine quasiparticle interference simulation (theory) and atomic
resolution scanning tunneling spectro-microscopy (experiment) to visualize the
interference patterns on a type-II Weyl semimetal MoWTe for
the first time. Our simulation based on first-principles band topology
theoretically reveals the surface electron scattering behavior. We identify the
topological Fermi arc states and reveal the scattering properties of the
surface states in MoWTe. In addition, our result reveals
an experimental signature of the topology via the interconnectivity of bulk and
surface states, which is essential for understanding the unusual nature of this
material.Comment: To appear in Phys. Rev. Let
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