Reduction Of Thermal Noise Research Articles

Reducing thermal noise in high-resolution quantitative magnetic resonance imaging rotating frame relaxation mapping of the human brain at 3 T.

Quantitative maps of rotating frame relaxation (RFR) time constants are sensitive and useful magnetic resonance imaging tools with which to evaluate tissue integrity in vivo. However, to date, only moderate image resolutions of 1.6 x 1.6 x 3.6 mm3 have been used for whole-brain coverage RFR mapping in humans at 3 T. For more precise morphometrical examinations, higher spatial resolutions are desirable. Towards achieving the long-term goal of increasing the spatial resolution of RFR mapping without increasing scan times, we explore the use of the recently introduced Transform domain NOise Reduction with DIstribution Corrected principal component analysis (T-NORDIC) algorithm for thermal noise reduction. RFR acquisitions at 3 T were obtained from eight healthy participants (seven males and one female) aged 52 ± 20 years, including adiabatic T1ρ, T2ρ, and nonadiabatic Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n = 4 (RAFF4) with both 1.6 x 1.6 x 3.6 mm3 and 1.25 x 1.25 x 2 mm3 image resolutions. We compared RFR values and their confidence intervals (CIs) obtained from fitting the denoised versus nondenoised images, at both voxel and regional levels separately for each resolution and RFR metric. The comparison of metrics obtained from denoised versus nondenoised images was performed with a two-sample paired t-test and statistical significance was set at pless than 0.05 after Bonferroni correction for multiple comparisons. The use of T-NORDIC on the RFR images prior to the fitting procedure decreases the uncertainty of parameter estimation (lower CIs) at both spatial resolutions. The effect was particularly prominent at high-spatial resolution for RAFF4. Moreover, T-NORDIC did not degrade map quality, and it had minimal impact on the RFR values. Denoising RFR images with T-NORDIC improves parameter estimation while preserving the image quality and accuracy of all RFR maps, ultimately enabling high-resolution RFR mapping in scan times that are suitable for clinical settings.

A review of application, modification, and prospect of melamine foam

Abstract Melamine foam (MF), a promising development in light materials, finds application in construction, agriculture, aviation, transportation, electronic message, and other fields due to its excellent thermal insulation performance, sound absorption and noise reduction capabilities, safety and health benefits, as well as easy processing. However, its own shortcomings such as hardness, poor toughness, fragility, and slag removal greatly limit its application scope. In this review, a survey of the literature from two aspects of toughening of melamine resin and regulation of MF pore structure are reviewed to explore the research progress of toughening modification of MF. The principle, merit, and demerit of different modification methods are analyzed. In addition, owing to the extensive literature available, this article also summarizes the representative achievements of the nanotechnology modification of MF derivatives (carbon foam and carbon aerogel). Eventually, based on an assessment of current application status for both MF and its derivatives while considering existing challenges in their modification processes using nanotechnology approaches, we discuss future prospects for their application.

Electron spin resonance spectroscopy using a Nb superconducting resonator

Recently, micro-resonator structures have demonstrated considerable enhancement of ESR spectroscopy. The high-quality factor and confined mode of these resonators (cavities) lead to an enhanced spin-cavity interaction that both increase sensitivity for conventional measurements and allow access to experiments that can investigate and utilize effects associated with strongly interacting spin ensembles and cavities. Superconducting micro-resonators are particularly interesting due to their natural compatibility with low temperatures, where the reduction of thermal noise permits coherent effects of the spin-cavity interaction to be resolved. In this work, we present X-band CW-ESR measurements of a microcrystalline BDPA sample performed using a niobium (Nb) superconducting micro-resonator. The achieved ultimate sensitivity and power conversion factor for this particular device, interfaced with an X-band Bruker EMX Micro ESR spectrometer, were found to be 5.4 × 108 Spins/G and 155 G/W, respectively, at a temperature of 3.8 K. The enhanced spin-cavity interaction in our setup had a profound influence on the measured BDPA spectral line shape, leading to a line-narrowing process not present in measurements performed using a conventional 3D resonator.

The Role of Urban Vegetation in Counteracting Overheating in Different Urban Textures

With growing global concerns about climate change, the significance of urban greenery in architecture and urban planning is becoming increasingly apparent. Urban vegetation naturally cools cities, provides comfort and clean air, and has positive social, health, and economic effects. It is essential to ensure passive thermal comfort and safeguard biodiversity. It is widely recognized that urban greenery not only withstands severe outdoor climatic events, but also symbiotically interacts with buildings and citizens. Several studies demonstrated the potential of vegetation to provide outdoor thermal comfort, air purification, noise reduction, and various other ecosystem services. To emphasize the potential of urban green spaces to interact with the local urban morphology in terms of microclimatic aspects, the research examines the dynamic connection between various urban textures and urban green spaces. This study emphasizes how urban green spaces, such as parks, green spaces, and urban greenery, respond to temperature variations in both the present scenario and the projected future. Central to this contribution is the examination of the relationship between urban vegetation and its potential to reduce and counteract urban overheating in both current and projected future scenarios. The aim is to evaluate the effectiveness of urban vegetation compared to dense urban textures. The interaction between urban block morphology, building types, vegetation, and microclimates is presented here for comparative assessment, highlighting the different thermal behaviour and outdoor comfort responses in various urban areas in current and projected scenarios. Using a microclimatic simulation tool, the research will delve deeper into the potential and constraints associated with the role of urban greens in addressing the increasing temperatures in climate change. This paper presents a comparative microclimatic evaluation of two selected green areas in Parma, Italy, within different urban contexts. The evaluation compares the current situation with a projected future scenario (2050) to determine the most effective factors for mitigating overheating phenomena in existing cities.

Polyimide/SiO2 composite aerogels with excellent thermal and sound insulation properties prepared by confined filling method

Aerogels have enormous potential in integrated thermal insulation and noise reduction applications. According to the knowledge of the favorable mechanical and acoustic properties of honeycomb structures. We employed anisotropic “honeycomb-like” polyimide (PI) aerogels as the matrix and utilized a confined filling strategy to directionally filled continuous SiO2 aerogels into the PI aerogel matrix. This resulted in the creation of an exceptional organic–inorganic composite aerogel (PISis) with outstanding thermal and acoustic insulation performance. The radial thermal conductivity of PISis ranged from 22.37 to 27.65 mW·m−1·K−1, and the initial decomposition temperature was approximately 524–557 °C. In the frequency range of 500–6300 Hz, the average sound transmission loss (STL) of the 18 mm thick composite material reached 30.67 ∼ 31.89 dB, and the compressive strength at 10 % strain is 0.416 MPa. The PISis exhibits a density ranging from 0.1012 to 0.1302 g/cm3. These make it an ideal lightweight, high-strength, and efficient material for thermal and acoustic insulation.

Unidirectional infiltrated PI/SiO2 composite aerogels with a confined reinforcing strategy for integrated thermal and acoustic insulation

It is of great significance to develop integrated thermal insulation and noise reduction materials for energy saving and pollution control. As a nanoporous material, aerogels have excellent thermal and acoustic properties, however, the thermal stability of organic aerogels is insufficient, and the mechanical properties of inorganic aerogels limit their practical application. Herein, we designed a confined reinforcing strategy for organic-inorganic composite aerogels with high strength and excellent acoustic insulation properties. A directional freezing technology was utilized to control the pore structure of a polyimide (PI) aerogel, and then a continuous SiO2 aerogel was filled in the unidirectional pore channels, forming a double-network structure consisting of both PI and SiO2 aerogels. The results showed that the compressive strength of the composites was 1.83 MPa at 10% strain, the initial thermal decomposition temperature was about 530 °C, and the lowest thermal conductivity was 22.37 mW m−1·k−1 at radial direction. Moreover, the average sound transmission loss (STL) of the composites with an 18 mm thickness was 30–33 dB in the range of 500–6300 Hz. This confined reinforcing strategy can safeguard fragile aerogels while maximize their inherent characteristics, which offers a novel approach to the creation of multi-functional aerogel composites.

A Review of Studies on Heat Transfer in Buildings with Radiant Cooling Systems

Due to their benefits in interior thermal comfort, energy saving, and noise reduction, radiant cooling systems have received wide attention. Radiant cooling systems can be viewed as a part of buildings’ maintenance structure and a component of cooling systems, depending on their construction. This article reviews studies on heat exchange in rooms utilizing radiant cooling systems, including research on conduction in radiant system structures, system cooling loads, cooling capacity, heat transfer coefficients of cooling surfaces, buildings’ thermal performance, and radiant system control strategy, with the goal of maximizing the benefits of energy conservation. Few studies have examined how radiant cooling systems interact with the indoor environment; instead, earlier research has focused on the thermal performance of radiant cooling systems themselves. Although several investigations have noted variations between the operating dynamics of radiant systems and conventional air conditioning systems, the cause has not yet been identified and quantified. According to heat transfer theory, the authors suggest that additional research on the performance of radiant systems should consider the thermal properties of inactive surfaces and that buildings’ thermal inertia should be used to coordinate radiant system operation.

Thermorefringent noise in crystalline optical materials

Crystalline materials are increasingly employed to construct precision optical instruments because of their reduced mechanical dissipation and consequent reduction of thermal Brownian noise. However, the anisotropy of the crystalline state implies a fundamental source of thermal noise; depolarization induced by thermal fluctuations of its birefringence. We establish the theory of this effect, which is a generalization of prior treatments of thermo-optic noises in amorphous materials. This theory---in conjunction with poorly understood anisotropic thermal stress coefficients of crystalline coatings---predict that thermo-refringent noise in crystalline mirror coatings may be lurking within an order of magnitude of Brownian noise (below 100 Hz). Thus, in order to appreciate the full promise of crystalline optical materials, a more precise understanding of their anisotropic material constants is necessary. Barring that, we elucidate measurement techniques that can affect partial coherent cancellation of thermorefringent noise. In passing, our general formalism also predicts the existence of thermal beam-pointing noise.

The seismic isolation system of Advanced Virgo Plus, Phase II

In 2025, the Advanced Virgo Plus (AdV+) gravitational-wave detector will enter Phase II, a thermal noise reduction upgrade involving the increase of the terminal mirror masses from 42 kg to 104 kg. This requires a revision of the SuperAttenuator (SA), the main attenuation system in AdV+, currently capable of reducing seismic noise by more than ten orders of magnitude in all six degrees of freedom above a few Hz. We briefly report the multiple updates of SA parts that have been planned to keep performance unchanged. As part of the study, simulations and/or design of upgraded elastic (maraging blades) and counter-elastic (magnetic antisprings) components were carried out, leading to a revision plan of all the filters in terminal SAs and notably of Filter 7 (F7), the lowest one. Prototyping and tests of the upgraded F7 and blades are underway at this time to validate the outputs of the study.

Squeezed States of Light for Future Gravitational Wave Detectors at a Wavelength of 1550nm.

The generation of strongly squeezed vacuum states of light is a key technology for future ground-based gravitational wave detectors (GWDs) to reach sensitivities beyond their quantum noise limit. For some proposed observatory designs, an operating laser wavelength of 1550nm or around 2 μm is required to enable the use of cryogenically cooled silicon test masses for thermal noise reduction. Here, we present for the first time the direct measurement of up to 11.5dB squeezing at 1550nm over the complete detection bandwidth of future ground-based GWDs ranging from 10kHz down to below 1Hz. Furthermore, we directly observe a quantum shot-noise reduction of up to (13.5±0.1) dB at megahertz frequencies. This allows us to derive a precise constraint on the absolute quantum efficiency of the photodiode used for balanced homodyne detection. These results hold important insight regarding the quantum noise reduction efficiency in future GWDs, as well as for quantum information and cryptography, where low decoherence of nonclassical states of light is also of high relevance.

Characterization of Laser Systems at 1550 nm Wavelength for Future Gravitational Wave Detectors

The continuous improvement of current gravitational wave detectors (GWDs) and the preparations for next generation GWDs place high demands on their stabilized laser sources. Some of the laser sources need to operate at laser wavelengths between 1.5 μm and 2.2 μm to support future detectors based on cooled silicon test masses for thermal noise reduction. We present detailed characterizations of different commercial low power seed laser sources and power amplifiers at the wavelength of 1550 nm with respect to performance parameters needed in GWDs. A combination with the most complete set of actuators was arranged as a master-oscillator power amplifier (MOPA), integrated into a stabilization environment and characterized. We present the results of this characterization that make this stabilized MOPA a highly relevant prototype for future GWDs as well as a low noise light source for other experiments in high precision metrology.

An efficient approach to fabricate lightweight polyimide/aramid sponge with excellent heat insulation and sound absorption performance

Polyimide sponges have bright prospects in the weight reduction, heat insulation, and sound absorption equipment of aerospace, navigation, and other area due to their unique three-dimensional cellular structure and outstanding comprehensive performance. However, most polyimide sponges suffered from long and complex fabrication processes. Herein, an efficient and scalable approach, i.e. water-based foam forming, was proposed to fabricate ultralight and porous polyimide/aramid sponges (PASG). Attributed to the bubble-template nature of foam-forming, PASGs exhibit high porosity (>99%) and ultra-low density (∼10 mg/cm3), and possess excellent thermal and sound insulation performance with an optimum thermal conductivity of 34.89 mW/m·K and noise reduction coefficient of 0.41. Besides, PASGs demonstrate outstanding mechanical properties after 500 compression cycles. This strategy providing more possibilities for developing the next generation of high-performance thermal insulation and noise reduction materials.

Thermal noise reduction in soliton microcombs via laser self-cooling.

Thermal noise usually dominates the low-frequency region of the optical phase noise of soliton microcombs, which leads to decoherence that limits many aspects of applications. In this work, we demonstrate a simple and reliable way to mitigate this noise by laser cooling with a pump laser. The key is rendering the pump laser to simultaneously excite two neighboring cavity modes from different families that are respectively red and blue detuned, one for soliton generation and the other for laser cooling.

Raw data for: Thermal noise reduction in soliton microcombs via laser self-cooling

Raw data for: Thermal noise reduction in soliton microcombs via laser self-cooling

Forty five nm CMOS low power multilevel active feedback transimpedance amplifier for optical receivers

PurposeRecent advancements in the domain of smart communication systems and technologies have led to the augmented developments for very large scale integrated circuit designs in electro-magnetic applications. Increasing demands for low power, compact area and superior figure of merit–oriented circuit designs are the trends of the recent research studies. Hence, to accomplish such applications intended for optical communications, the transimpedance amplifier (TIA) was designed.Design/methodology/approachIn this research work, the authors present a multi-layer active feedback structure which mainly composes a transimpedance stage and a gain stage followed by a low pass filter. This structure enables to achieve improved input impedance and superior gain. A simplified cascaded amplifier has also been designed in a hierarchical topology to improvise the noise effect further. The proposed TIA has been designed using Taiwan Semiconductor Manufacturing Company 45 nm complementary metal oxide semiconductor technology. Moreover, the thermal noise has been analyzed at −3 dB bandwidth to prove the reduction in thermal noise with increase in frequency for most of the devices used in the designed circuit.FindingsThe proposed differential TIA circuit was found to obtain the transimpedance gain of 50.1 dBO without applying any external bias current which is almost 8% improvised as compared to the conventional circuit. In addition to this, bandwidth achieved was 2.15 GHz along with only 38 W of power consumption, which is reasonably 100 times improvised in comparison of conventional circuit. Hence, the proposed differential TIA is suitable for the low power optical communications applications intended to work on low supply voltage.Originality/valueThe designed work is done by authors in university lab premises and is not copied from anywhere. To the best of the authors’ knowledge, it is 100% original.

Ternary quarter wavelength coatings for gravitational wave detector mirrors: Design optimization via exhaustive search

Multimaterial optical coatings are a promising viable option to meet the challenging requirements (in terms of transmittance, absorbance and thermal noise) of next generation gravitational wave detector mirrors. In this paper we focus on ternary coatings consisting of quarter-wavelength thick layers, where a third material (H') is added to the two presently in use, namely Silica (L) and Titania-doped Tantala (H), featuring higher dielectric contrast (against Silica), and lower thermal noise (compared to Titania-doped Tantala), but higher optical losses. We seek the optimal material sequences, featuring minimal thermal (Brownian) noise under prescribed transmittance and absorbance constraints, by exhaustive simulation over all possible configurations, for different values (in a meaningful range) of the optical density and extinction coefficient of the third material. In all cases studied, the optimal designs consist of a stack of (H'|L) doublets topped by a stack of (H|L) doublets, confirming previous heuristic assumptions, and the achievable coating noise power spectral density reduction factor is \sim 0.5. The robustness of the found optimal designs against layer thickness deposition errors and uncertainties and/or fluctuations in the optical losses of the third material is also investigated. Possible margins for further thermal noise reduction by layer thickness optimization, and strategies to implement it, are discussed.

Projection imaging with ultracold neutrons

Ultracold neutron (UCN) projection imaging is demonstrated using a boron-coated back-illuminated CCD camera and the Los Alamos UCN source. Each neutron is recorded through the capture reactions with10B. By direct detection at least one of the byproducts α, 7Li and γ (electron recoils) derived from the neutron capture and reduction of thermal noise of the scientific CCD camera, a signal-to-noise improvement on the order of 104 over the indirect detection has been achieved. Sub-pixel position resolution of a few microns is confirmed for individual UCN events. Projection imaging of test objects shows a spatial resolution less than 100μm by an integrated UCN flux one the order of 106 cm−2. The bCCD can be used to build UCN detectors with an area on the order of 1 m2. The combination of micrometer scale spatial resolution, low readout noise of a few electrons, and large area makes bCCD suitable for quantum science of UCN.

Cryogenic suspension design for a kilometer-scale gravitational-wave detector

We report the mirror suspension design for large-scale cryogenic gravitational wave telescope, KAGRA, during bKAGRA phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA phase 1 are discussed.

Higher-order Hermite-Gauss modes for gravitational waves detection

As part of the research on thermal noise reduction in gravitational-wave detectors, we experimentally demonstrate the conversion of a fundamental ${\mathrm{TEM}}_{00}$ laser mode at 1064 nm to higher-order Hermite-Gaussian modes (HG) of arbitrary order via a commercially available liquid crystal spatial light modulator. We particularly studied the ${\mathrm{HG}}_{5,5}/{\mathrm{HG}}_{10,10}/{\mathrm{HG}}_{15,15}$ modes. A two-mirror plano-spherical cavity filters the higher-order modes spatially. We analyze the cleaned modes via a three-mirror diagnosis cavity and measure a mode purity of $96/93/78%$ and a conversion efficiency of $6.6%/3.7%/1.7%$, respectively. A full set of simulations and mathematical proofs are also presented which shows that (i) Hermite-Gauss modes resonate in a two-mirror cavity provided mirrors are properly angled with respect to the impinging mode, and (ii) Hermite-Gauss modes resonate in triangular cavities. Hence, higher-order Hermite-Gauss modes are compatible with ground-based gravitational-wave detectors' architecture and can be employed for the mitigation of mirror thermal noise for the third generation Einstein Telescope or Cosmic Explorer.

Higher-order Hermite-Gauss modes as a robust flat beam in interferometric gravitational wave detectors

Higher-order Laguerre-Gauss (LG) modes have previously been investigated as a candidate for reducing test-mass thermal noise in ground-based gravitational-wave detectors like Advanced LIGO. It has been shown however that LG modes' fragility against mirror surface figure imperfections limits their compatibility with the current state-of-the-art test masses. In this paper we explore the alternative of using higher-order Hermite-Gauss (HG) modes for thermal noise reduction, and show that with the deliberate addition of astigmatism they are orders of magnitude more robust against mirror surface distortions than LG modes of equivalent order. We present simulations of Advanced LIGO-like arm cavities with realistic mirror figures which can support HG$_{33}$ modes with average arm losses and contrast defects in a Fabry-Perot Michelson interferometer configuration which are well below the typical measured values in Advanced LIGO. This demonstrates that the mirror surface flatness errors will not be a limiting factor for the use of these modes in future gravitational-wave detectors.