Addressing the self-interaction for ELDER dark matter from the 21-cm signal

The self-interacting dark matter can affect various cosmological processes. Such interactions can be number conserving (\emph{e.g.} $2 \rightarrow 2$) or number violating (\emph{e.g.} $3 \rightarrow 2,\,4 \rightarrow 2$ etc.). The latter processes where three (or more) dark matter particles undergo self-annihilation/scattering to produce less number of dark matter is termed as ``Cannibalism'' process. In this work, the self-interaction of dark matter and the strength of such interactions are investigated in the light of experimental results of the global 21-cm spectrum of neural hydrogen from the era of cosmic dawn. From the present work, it appears that $2\rightarrow 2$ process is much more dominant over the $3\rightarrow 2$ process. It is also found that such interactions affect the dark matter-baryon elastic scattering cross-section. The study also indicates the presence of multi component dark matter of different mass range in the Universe.Comment: 19 pages, 5 figure

D-band medium power traveling wave tube

D-band (141 - 175.8 GHz) is very attractive for high capacity wireless links. However, the low power available from solid state amplifiers is not sufficient to ensure long links with 99.99% availability in the most common rain zones. Traveling wave tubes have been extensively demonstrated as the solution for satisfying the link budget. At sub-THz frequencies their fabrication is difficult and expensive. Typically, the 40 dB gain needed can be provided by two sections of slow wave structure separated by a sever. Due to the intrinsic low interaction impedance at sub-Thz frequencies, slow wave structures with high number of periods are needed. In case of metal SWS this determines long fabrication time and difficult assembly. This paper presents a short double corrugated waveguides for wide band (141 - 148.5 GHz) TWTs to provide about 26 dB gain and reduced fabrication difficulties

Adverse effects of temperature on perinatal and pregnancy outcomes: methodological challenges and knowledge gaps

Evidence linking temperature with adverse perinatal and pregnancy outcomes is emerging. We searched for literature published until 30 January 2023 in PubMed, Web of Science, and reference lists of articles focusing on the outcomes that were most studied like preterm birth, low birth weight, stillbirth, and hypertensive disorders of pregnancy. A review of the literature reveals important gaps in knowledge and several methodological challenges. One important gap is the lack of knowledge of how core body temperature modulates under extreme ambient temperature exposure during pregnancy. We do not know the magnitude of non-modulation of body temperature during pregnancy that is clinically significant, i.e., when the body starts triggering physiologic counterbalances. Furthermore, few studies are conducted in places where extreme temperature conditions are more frequently encountered, such as in South Asia and sub-Saharan Africa. Little is also known about specific cost-effective interventions that can be implemented in vulnerable communities to reduce adverse outcomes. As the threat of global warming looms large, effective interventions are critically necessary to mitigate its effects

Design of sub-THz traveling wave tubes for high data rate long range wireless links

The development of high capacity wireless networks, to satisfy the increasing demand of mobile high-speed internet, is stimulating the exploitation of the wide frequency bands in the millimeter and THz range. Above 100 GHz, the high atmosphere attenuation is the major obstacle for wireless links of adequate length, due to the low power available from solid state amplifiers. Traveling wave tubes are promising devices capable to generate multi-watt power at sub-THz frequency. In this paper, the design and performance of a Traveling Wave Tube in the 210 – 250 GHz band with about 1W output power will be described, to power a 40 Gigabits per second optical transmitter for 1 km point-to-point link. A novel approach for a simple and low-cost fabrication, based on the use of the double corrugated waveguide is proposed

Sensitivity analysis of a double corrugated waveguide slow wave structure for a 151 - 161.5 GHz TWT

TWTs at D-band (141 – 174.5 GHz) are the most promising solution to provide high transmission power for enabling long range wireless links with high capacity at sub-THz frequency. A D-band TWT was designed in the 151-161.5 GHz frequency band with about 10 W output power. The double corrugated waveguide is adopted as slow wave structure (SWS) for the relatively easy fabrication and alignment in comparison to other SWSs typically used at sub-THz frequency. Due to the short wavelength at D-band, the fabrication requires high precision computerised numerically controlled (CNC) milling machining and tight tolerance control. The sensitivity analysis of performance as a function of the dimensions of a device is an important method to predict in advance how the performance of the device is affected by geometry variations, and also to ascertain the required level of fabrication accuracy to meet the specifications. The sensitivity analysis is also useful to define the best initial dimensions for further optimization. This paper discusses the sensitivity analysis applied to the double corrugated waveguide (DCW) to be used in a 151-161.5 GHz TWT. A broad range of parameters are considered demonstrating the importance of fabrication accuracy and the eventual correction options for a correct functioning. The impact of fillets in the DCW pillars is also evaluated to eventually ease the fabrication requirement

E-band traveling wave tube for high data rate wireless links

E-band (71 – 76 GHz and 81 – 86 GHz) is already used for point to point links with a few Gigabit/second data rate. Front-ends are powered by solid state amplifiers with about 2 – 3 W output power. This output power values limit range and spectral efficiency and have to be compensated by high gain antennas. The availability of tens of Watt would allow higher spectral efficiency and long range, and the use of lower gain antennas for multibeam and area coverage. This paper reports the design and the initial fabrication of the first ever E-band Traveling Wave Tube (TWT) based on the double corrugated waveguide. A test short interaction structure TWT is in assembly phase as proof of concept with about 2 W output power. The final TWT is designed to provide about 70 W power and about 40 dB gain