THE difficulty of reconciling line spectra with the kinetic theory of gases, has been referred to by Prof. Fitzgerald (NATURE, January 3, p. 221). The following considerations show that it is possible under certain suppositions to have a number of spectral rays with a very restricted number of degrees of freedom. Most of us, I believe, now accept a definite atomic charge of electricity, and if each charge is imagined to be capable of moving along the surface of an atom, it would represent two degrees of freedom. If a molecule is capable of sending out a homogeneous vibration, it means that there must be a definite position of equilibrium of the “electron.” If there are several such positions, the vibrations may take place in several periods. Any one molecule may perform for a certain time a simple periodic oscillation about one position of equilibrium, and owing to some impact the electron may be knocked over into a new position. The vibrations under these circumstances would not be quite homogeneous, but if the electron oscillates about any one position sufficiently long to perform a few thousand oscillations, we should hardly notice the want of homogeneity. Each electron at a given time would only send out vibrations which in our instruments would appear as homogeneous. Each molecule could thus successively give rise to a number of spectral rays, and at any one time the electron in the different molecules would, by the laws of probability, be distributed over all possible positions of equilibrium, so that we should always see all the vibrations which any one molecule of the gas is capable of sending out. The probability of an electron oscillating about one of its positions of equilibrium need not be the same in all cases. Hence a line may be weak not because the vibration has a smaller amplitude, but because fewer molecules give rise to it. The fact that the vibrations of a gas are not quite homogeneous, is borne out by experiment. If impacts become more frequent by increased pressure, we should expect from the above views that the time during which an electron performs a certain oscillation is shortened; hence the line should widen, which is the case. I have spoken, for the sake of simplicity, as if an electron vibrating about one position of equilibrium could only do so in one period. If the forces called into play, by a displacement, depend on the direction of the displacement, there would be two possible frequencies. If the surface is nearly symmetrical, we should have double lines.

/pdf/the-kinetic-theory-of-gases-13lklkm24y.pdf

The Kinetic Theory of Gases

Plasmonic refractive index sensing in the early diagnosis of diabetes, anemia, and cancer: An exploration of biological biomarkers

Diabetes mellitus is linked to both short-term and long-term health problems. Therefore, its detection at a very basic stage is of utmost importance. Research institutes and medical organizations are increasingly using cost-effective biosensors to monitor human biological processes and provide precise health diagnoses. Biosensors aid in accurate diabetes diagnosis and monitoring for efficient treatment and management. Recent attention to nanotechnology in the fast-evolving area of biosensing has facilitated the advancement of new sensors and sensing processes and improved the performance and sensitivity of current biosensors. Nanotechnology biosensors detect disease and track therapy response. Clinically efficient biosensors are user-friendly, efficient, cheap, and scalable in nanomaterial-based production processes and thus can transform diabetes outcomes. This article is more focused on biosensors and their substantial medical applications. The highlights of the article consist of the different types of biosensing units, the role of biosensors in diabetes, the evolution of glucose sensors, and printed biosensors and biosensing systems. Later on, we were engrossed in the glucose sensors based on biofluids, employing minimally invasive, invasive, and noninvasive technologies to find out the impact of nanotechnology on the biosensors to produce a novel device as a nano-biosensor. In this approach, this article documents major advances in nanotechnology-based biosensors for medical applications, as well as the hurdles they must overcome in clinical practice.

https://www.mdpi.com/2079-4991/13/5/867/pdf?version=1677556667

A Nanotechnology-Based Approach to Biosensor Application in Current Diabetes Management Practices

In this article, we review optical MEMS accelerometers with a particular focus on sensing techniques and interrogation methods. Optical accelerometers find use in various application domains ranging from microgravity to inertial navigation to vibration sensing. The performance of an accelerometer is quantified in terms of its range, bandwidth, sensitivity, and resolution. The combination of sensing technique and interrogation method determines the optical accelerometer’s performance. This article presents a classification in terms of guided-wave and free-space based optical sensing techniques used in acceleration measurement and their review. In free-space based sensing techniques, light propagating in free-space interacts with the mechanical structure resulting in modification of light properties at the receiver. In guided-wave based sensing techniques, light interaction with the mechanical structure is confined to the waveguide. Also, the different interrogation methods used in optical MEMS accelerometers are reviewed. The interrogation methods are classified as based on intensity modulation or frequency modulation of the optical signal received from sensor. In intensity-modulation based interrogation, light intensity at output is the measurand and, the cost and complexity of this class of methods is lower. In frequency-modulation based interrogation, the frequency or phase of the optical signal at the output is the measurand. Further, a high-resolution optical MEMS accelerometer based on waveguide Bragg gratings is described. A combination of free-space based sensing and intensity-modulation based interrogation methods will be suitable for consumer-grade accelerometer applications. For high-resolution applications like tactical and navigation grades, a combination of guided-wave sensing and frequency-modulation based interrogation methods would be appropriate.

Sensing Techniques and Interrogation Methods in Optical MEMS Accelerometers: A Review

This paper is a report on the design and fabrication of a dual-axis micro-opto-electro-mechanical system (MOEMS) accelerometer. The device consists of a proof mass (PM) suspended by four L-shaped springs. Two Fabry-Perot (FP) cavities are formed between the cross-sections of the PM and the ends of two cleaved optical fibers in perpendicular directions (the X and Y axes). The acceleration causes the proof mass to move in the reverse direction relative to the applied acceleration. The sensor is fabricated by a silicon-on-insulator wafer. The fabricated sensor is characterized both by spectral monitoring and power measurements in the range of ±1 g. The results of spectral measurements show 3.23 nm/g (g = 9.81 m/s2: gravity constant) and 3.19 nm/g to the applied acceleration along the X and Y axes, respectively. Moreover, the obtained resolutions for the two directions of X and Y are $309~\mu \text{g}$ and $313~\mu \text{g}$ , respectively. Besides, the sensitivity of the sensor in power measurements is 550 mV/g and 528 mV/g in the X and Y directions, respectively. The sensor also possesses the resonant frequencies of 1382.5 Hz and 1398.6 Hz in the X and Y axes, respectively, in the range of ±1 g. The maximum cross-axis sensitivities obtained for this sensor are below 0.19% for each pair of X, Y, and Z axes. This value is fewer than the cross-axis sensitivity of most micro electro-mechanical systems without any post processing. This small value is a result of insensitivity of the FP spectrum to the lateral displacements of the PM.

A Dual-Axis MOEMS Accelerometer

A simulation and analysis of a ring resonator-based sensor are presented. The ring resonator structure has two bus waveguides and two rings with a gap between the ring and the ring and bus waveguide. The radius of each ring is designed to be 3.1  μm. The ring resonator is designed such that both rings exhibit resonance at 1550 nm, and it is analyzed at mid-infrared wavelengths between 1500 and 1600 nm. The guided signal is launched through the bus waveguide to determine spectral properties, such as free spectral range and quality (Q-) factor. An improved Q-factor is observed in the simulation results for the optimized design. The improved Q-factor allows us to analyze the ring resonator for use in sensing applications.

Improvement in quality factor of double microring resonator for sensing applications

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 μ g/ Hz and is suitable for inertial navigation and seismometry applications.

Novel High-Resolution Lateral Dual-Axis Quad-Beam Optical MEMS Accelerometer Using Waveguide Bragg Gratings

Survey on various architectures of preamplifiers for electroencephalogram (EEG) signal acquisition

Design and analysis of high-sensitivity optical MEMS accelerometer based on waveguide Bragg grating integrated with Crab-leg beam for low frequency applications is presented in this paper. Crab-leg beam are used to suspend the proof-mass to decrease spring stiffness with low device footprint. A waveguide Bragg grating is positioned on the shin of crab-leg to maximize strain sensitivity. To compensate for the temperature dependence of Bragg spectral properties, a reference grating positioned on the proof-mass is used. Due to excellent linear response, high-sensitivity of 184 pm/g and low fundamental frequency, the proposed accelerometer is suitable for microgravity and seismometry applications.

Optical MEMS Accelerometer Based on Waveguide Bragg Grating Integrated with Crab-Leg Beam

In this work modeling and analysis of an integrated opto-fluidic sensor, with a focus on achievement of single mode optical confinement and continuous flow of microparticles in the microfluidic channel for lab-on-a-chip (LOC) sensing application is presented. This sensor consists of integrated optical waveguides, microfluidic channel among other integrated optical components. A continuous flow of microparticles in a narrow fluidic channel is achieved by maintaining the two sealed chambers at different temperatures and by maintaining a constant pressure of 1 Pa at the centroid of narrow fluidic channel geometry. The analysis of silicon on insulator (SOI) integrated optical waveguide at an infrared wavelength of 1550 nm for single mode sensing operation is presented. The optical loss is found to be 5.7 × 10−4 dB/cm with an effective index of 2.3. The model presented in this work can be effectively used to detect the nature of microparticles and continuous monitoring of pathological parameters for sensing applications.

https://www.mdpi.com/2072-666X/9/3/134/pdf

Modeling and Analysis of an Opto-Fluidic Sensor for Lab-on-a-Chip Applications

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