Efficient spontaneous emission by metal-dielectric antennas; antenna Purcell factor explained.

The rate of spontaneous emission from an optical emitter can be greatly enhanced using a metallic optical antenna at the penalty of efficiency. In this paper we propose a metal-dielectric antenna that eliminates the tradeoff between spontaneous emission enhancement and radiative efficiency by using nanoscopic dielectric structures at the antenna tips. This tradeoff occurs due to Ohmic loss and is further exacerbated by electron surface collisions. We find that our metal-dielectric antenna can enhance spontaneous emission by a factor 5 × 105 with efficiency = 70%, greatly exceeding the radiative efficiency of a purely metallic antenna with similar enhancement. Moreover, the metal-dielectric antenna design strategy is naturally amenable to short-distance optical communications applications. We go on to discuss the Purcell effect within the context of antenna enhancement. Metallic optical antennas are best analyzed with conventional antenna circuit models, but if the Purcell enhancement were to be employed, we provide the effective mode volume, Veff = (3/4π2)2d2λ(λ/l)5, that would be needed.

Inverse design optimization for efficient coupling of an electrically injected optical antenna-LED to a single-mode waveguide.

Efficient high-speed nanoscale optical sources are required for low-power next-generation data communication. Here we propose an integrated antenna-LED on a single-mode optical waveguide. By leveraging inverse design optimization, we achieved a waveguide coupling efficiency of 94% and an antenna efficiency of 64%, while maintaining a high average enhancement of 144 - potentially enabling >100GHz direct modulation.

Second harmonic generation in nano-structured thin-film lithium niobate waveguides.

Integrated thin-film lithium niobate platform has recently emerged as a promising candidate for next-generation, high-efficiency wavelength conversion systems that allow dense packaging and mass-production. Here we demonstrate efficient, phase-matched second harmonic generation in lithographically-defined thin-film lithium niobate waveguides with sub-micron dimensions. Both modal phase matching in fixed-width waveguides and quasi-phase matching in periodically grooved waveguides are theoretically proposed and experimentally demonstrated. Our low-loss (~3.0 dB/cm) nanowaveguides possess normalized conversion efficiencies as high as 41% W-1cm-2.

Climatic niche convergence through space and time for a potential archaeophyte (Acacia caven) in South America.

Based on the niche conservatism hypothesis, i.e. the idea that niches remain unchanged over space and time, climatic niche modelling (CNM) is a useful tool for predicting the spread of introduced taxa. Recent advances have extended such predictions deeper in time for plant species dispersed by humans before the modern era. The latest CNMs successfully evaluate niche differentiation and estimate potential source areas for intriguing taxa such as archaeophytes (i.e., species introduced before 1492 AD). Here, we performed CNMs for Acacia caven, a common Fabaceae tree in South America, considered an archaeophyte west of the Andes, in Central Chile. Accounting for the infraspecific delimitation of the species, our results showed that even when climates are different, climatic spaces used by the species overlap largely between the eastern and western ranges. Despite slight variation, results were consistent when considering one, two, or even three-environmental dimensions, and in accordance with the niche conservatism hypothesis. Specific distribution models calibrated for each region (east vs west) and projected to the past, indicate a common area of occupancy available in southern Bolivia-northwest Argentina since the late Pleistocene, which could have acted as a source-area, and this signal becomes stronger through the Holocene. Then, in accordance with a taxon introduced in the past, and comparing regional vs continental distribution models calibrated at the infraspecific or species level, the western populations showed their spread status to be mostly in equilibrium with the environment. Our study thus indicates how niche and species distribution models are useful to improve our knowledge related to taxa introduced before the modern era.

Paroxysmal Atrial Fibrillation (PFA) Detection With Cardiac Monitoring Devices Implanted by Neurologists in Patients With Embolic Strokes of Undetermined Source (ESUS).

Introduction Ischemic stroke is among the leading causes of death and disability. Approximately 50% of cryptogenic strokes are embolic strokes of undetermined source (ESUS). The most common cause of ESUS is atrial fibrillation. Therefore, the detection of atrial fibrillation with long-term implantable devices is needed. Neurologists are directly involved with acute and post-acute stroke care and have direct access to the management of stroke patients. Therefore, there is a need for neurologists to recommend, implant, and monitor cardiac implantable devices in patients with ESUS. Methods From November 2022 to October 2023, our group implanted 32 ESUS patients with Confirm Rx™ insertable cardiac monitors (Abbott, USA). Atrial fibrillation detection was supervised and monitored daily. Results In 24 months, atrial fibrillation was detected in 12.5% of patients (four patients), sinus bradycardia in 6.25% of patients (two patients), paroxysmal supraventricular tachycardia in 9.4% of patients (three patients), and asystole in one patient. Conclusion Our study shows that neurologists involved in the treatment of stroke care can safely implant, monitor, and detect atrial fibrillation accurately. Our rate of detection of atrial fibrillation in patients with ESUS was 12.8%, which is consistent with prior studies.

Detecting Cognitive Decline and Dementia in Santa Cruz, Galápagos Islands, Ecuador.

Objective To assess the cognitive function, prevalence, and risk factors associated with cognitive decline and dementia in people above 65 years of age in Santa Cruz Island, Galápagos, Ecuador.  Methods This is a cross-sectional observational study that was carried out in adults over 65 years of age in Santa Cruz Island, Galápagos, Ecuador. The mini-mental state examination (MMSE) and ascertain dementia eight-item informant questionnaire (AD8)-validated Ecuador Spanish versions were used to assess cognition. Results There were a total of 80 participants, 55 (67%) women and 25 (31.2%) men. The majority of participants were Mestizos (85.3%), with the remainder classified as White (4.8%), Afro-Ecuadorians (2.4%), or Indigenous (3.6%). The prevalence of cognitive impairment is 30.0%-43.7%. The MMSE results showed that older age and lack of education are risk factors for cognitive decline (p < 0.01). There was high correlation between MMSE and AD8 scores. The AD8 showed that older age, widowhood, and living in Santa Rosa were risk factors for cognitive decline (p < 0.01). According to the AD8, the group with the highest education (six years or more) had the lowest risk of cognitive decline and dementia (p < 0.01).  Conclusions The main risk factors for cognitive decline and dementia in individuals above 65 years old in Santa Cruz Island, Galápagos, Ecuador are increased age, lack of education, and widowhood. The prevalence of cognitive impairment is similar to previous studies in Ecuador.