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Numerical modelling of ultra low frequency waves in Earth's magnetosphere

Numerical modelling of ultra low frequency waves in Earth's magnetosphere

To begin to tackle the subject of this thesis, we discuss some of the general properties of what are now termed Ultra Low Frequency (ULF) waves, but were previously in the literature referred to as geomagnetic pulsations or micropulsations. A more specific intro- duction to the previous work on ULF waves relevant to this thesis is reserved for Section 1.6 of this introduction, after some of the prerequisite fundamental theory has been intro- duced in the sections to follow. ULF waves are low frequency oscillations of the Earth’s magnetic field which are typically small in amplitude compared to the background field strength. Some of the earliest observations of ULF waves date back to the Carrington event of 1859, when a coronal mass ejection collided with the magnetosphere triggering one of the most powerful geomagnetic storms on record. The oscillations of the Earth’s magnetic field were recorded by Stewart [1861], noting periods of a few minutes. It was not until 1964 that these oscillations were formally classified dependent on their frequency and wave form [Jacobs et al., 1964]. ULF waves are split into two categories: Pc for continuous pulsations and Pi for more irregular pulsations. In this thesis we discuss Pc pulsations, which are further subdivided into five classes dependent on their frequency, spanning frequencies from 1mHz to 1Hz or periods from 1000 seconds to 1 second. ULF waves are generated in the magnetosphere in a variety of ways. These generation mechanisms are best separated as either internal or external to the magnetosphere. Two external sources that will receive particular attention here due to their relevance to the work in this thesis are the Kelvin-Helmholtz (KH) instability of the magnetospheric flanks and solar wind dynamic pressure driving. A good summary of some of the other gener- ation mechanisms is given in the review by McPherron [2005]. Beginning with the KH instability, Southwood [1968] first showed that ULF waves could be generated by a shear flow instability of the magnetospheric flanks. Much like the wind causing surface waves on the ocean, the fast magnetosheath flow compared to the slower interior magnetospheric flow could cause magnetopause surface waves to develop. Southwood [1968] considered the mathematical treatment of this, using two perfectly conducting fluids separated by a thin boundary layer. Conditions for stability and the polarization of disturbances were derived, but not until later work (which will be discussed in Section 1.5) was this gener- ation mechanism fully linked to observed ULF modes. Since then, the (KH) instability has received much treatment and has been widely accepted as one of the main generation mechanisms of ULF waves in the magnetosphere.
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Gap Mesh Wire Control on Nano Particles Growth

Gap Mesh Wire Control on Nano Particles Growth

Ultra low frequency of plasma (ULFP) discharge has been experimentally investigated at very low pressure 0.6 mbar and a small distance between electrodes to distinguish between the two different glow discharges produced by two different cathode electrode configurations of a perforated aluminum (Al) wire meshes through measuring plasma parameters for both cases such as current temporal variations, breakdown voltages, and applied electric field values.

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Advances in Low Temperature Processing

Advances in Low Temperature Processing

Abstract --- Food is preserved by various methods such as high temperature processing (heating, blanching), low temperature processing (freezing) or by using chemicals. This paper reviews about novel technologies applied to low temperature freezing process like pulsed electric field treatment, high pressure processing, ultra sound freezing, ultra rapid freezing and pressure shift freezing. Low temperature freezing changes water (present in food) into ice in the number of crystals. Due to applied pressure, electric current and voltage small ice crystals are formed which are uniformly distributed to whole food. Hence, foods shelf life increases. Colour, texture, structure, taste, appearance and quality attributes are better preserved in freezing. Low temperature processing offers several advantages such as preservation of color, flavor, texture, appearance and volatile retention, modification of sensory qualities and inhibition of bacterial growth. Novel technologies applied to thawing like high voltage electric field thawing, radio frequency thawing and ultra sound assisted thawing have also explained. Thawing is process of conversion of frozen ice into liquid i.e. frozen ice crystals into water. Heat is supplied to frozen food which converts frozen food into unfrozen. Hence, these novel technologies have become beneficial in terms of preserving food and quality attributes & sensory characteristics.
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CalMagNet – an array of search coil magnetometers monitoring ultra low frequency activity in California

CalMagNet – an array of search coil magnetometers monitoring ultra low frequency activity in California

Fig. 3. Characteristics of a single ANT/4 magnetometer. (a) Plot of gain versus frequency for the ANT/4, pre-amplifier, and filter. (b) Noise floor of the ANT/4 magnetometer. These are measured values from coils deployed in CalMagNet. They were obtained by taking two coils to a remote, low-noise location, and differencing the signals to remove common mode signal while leaving only the internal noise of the system. Values differ slightly from Table 3 due to local environmental noise conditions during this particular test.

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Modulation of the orthostatic blood pressure response by acute nitrate consumption is dependent upon ethnic origin

Modulation of the orthostatic blood pressure response by acute nitrate consumption is dependent upon ethnic origin

Hypertension is possibly the leading cause of morbidity and mortality worldwide and hypertension in adolescence contributes to early death 1 and was a direct cause of death in 1% of the population in the United Kingdom 2 . Therefore, steps to ameliorate hypertension offer benefits to health and quality of life in all populations. Indeed, antihypertensives represented 20% of all prescriptions in the UK in 2013 3 . However, control of blood pressure in response to environmental factors such as gravity can present particular problems 4,5 especially with increasing age 6 . More recently dietary interventions, including diets rich in fruit and vegetables 7,8 were reported to decrease systemic blood pressure. The active agents in such diets have included inorganic nitrate 9,10 . Indeed, in large populations regular inorganic nitrate consumption decreased diastolic blood pressure. Furthermore, nitrate consumption increased efficiency of oxygen utilisation in skeletal muscle and hence
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Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

The primary aim of developing the AWESOME tech- nique was to analyse the entire ULF wave spectra and provide an estimate of uncertainty in the onset time, in addition to setting an objective and quantitative onset criteria. We note here that there is no overlap in uncer- tainty between the onsets of the different ULF wave bands, demonstrating that the onset of Pi1-2 waves occurs prior to Pi2 waves, and both occur prior to the higher frequency Pi1 wave band consistent with previ- ous studies at single stations (Murphy et  al. 2009a, b; Rae et al. 2009a, b; Walsh et al. 2010). We conclude that the Pi1-2 waves are linked to the formation and evolu- tion of auroral beads and are therefore onset driven (e.g. Rae et al. 2009a, b), whereas the longer period Pi2 waves may be related to the evolution of the large-scale cur- rent system that develops following onset, most likely the substorm current wedge (e.g. McPherron et al. 1973; Rae et  al. 2007; Murphy et  al. 2013). The timing differ- ence between auroral beads and auroral breakup during which the SCW begins to form is similar to timing differ- ence between the onset of the Pi1-2 and Pi2 wave bands; beads and Pi1/2 waves occurring contemporaneously and auroral breakup and Pi2 waves occurring 2–3 min later. This further supports our conclusion that Pi1-2 waves are linked to the auroral beads and Pi2 waves are linked to the SCW. Presumably in this scenario, Pi1 waves cor- respond to the later structuring and filamentation of the current systems that develop into auroral breakup (e.g. Arnoldy et al. 1987; Bösinger 1989).
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Designing a Carbon Nanotube Field Effect Transistor with High Transition Frequency for Ultra Wideband Application

Designing a Carbon Nanotube Field Effect Transistor with High Transition Frequency for Ultra Wideband Application

Figure 4 shows the effect of changing the diameter on the capacitors of the circuit (quantum capacitor (CQ), electrostatic capacitor (C-SIG) and effective capacitor (cgs)), in the FETToy model. In FETToy model, the gate structure is cylindrical, Equation (1.a), indicates the formula for calculating the value of gate capacitor, thereby, increasing the diameter of the circuit, the capacitor surface has increased, and the value of electrostatic capacitor of the circuit, has increased (It should be noted, these results are derived for cylindrical structure, and for the different structures, different results may be achieved). Quantum capacitor, in- dicating the relationship between the change of channel potential and the carri- ers density, which decreases with increasing diameter; or in other word, the po- tential impact on carrier density is reduced, this may mean reduction of gate control on the channel. Effective capacitor, that represents the effects of all the capacitors, is increased; while its increase has lower slope than the curve of the electrostatic capacitor. According to Equation (2.a), increasing the effective ca- pacitor means to lower transition frequency. Figure 5 shows the effect of chang- ing the diameter of the nanotube on the transconductance, in the simulation with FETToy. Diameter increases is associated with increase in transconduc- tance. In this figure the transconductance increases from 0.24 μ in diameter 0.4 nm to 0.97 μ  in diameter 3.6 nm.
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Fine structure of the low-frequency spectra of heart rate and blood pressure

Fine structure of the low-frequency spectra of heart rate and blood pressure

The existence of two or more distinct oscillatory compo- nents in the LF band was a striking observation. In the literature there are no specific reports of multiple spectral components in this frequency band in humans. In most cases the explanation is very simple: overall spectral power has been used as a measure of sympathetic activity, and detailed spectral composition has not been the target of the studies. It is very difficult to distinguish close spectral peaks using FFT analysis when sliding time win- dows are not used. Previous studies that have used AR modeling employed model orders that were too low to allow close peaks to be discriminated, as we have demon- strated. However, in animal studies there are some inter- esting reports on the presence of two spectral peaks within the LF band. Cevese et al. [15] investigated spontaneous fluctuations in heart rate and blood pressure in anesthe- tized dogs with the left iliac vascular bed mechanically uncoupled from the central circulation. They found indi- vidual peaks in RRI and SAP spectra at 0.03–0.07 Hz and at 0.12–0.17 Hz, and in some cases there was
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Ultra High Frequency Oscillators

Ultra High Frequency Oscillators

The curves on p.12 show the change of the plate current as a function of the displacement of electrodes with respect to the position of the loop of the voltage wave expressed in percent [r]

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Design of RF amplifier and LPF for low magnetic field and low frequency NMR Spectrometer

Design of RF amplifier and LPF for low magnetic field and low frequency NMR Spectrometer

Aktham Asfour had been designed and development of a new home-built NMR spectrometer working at very-low magnetic field (4.5 mT). This spectrometer allows detection and acquisition of NMR proton (H) signals. It consists of a resistive magnetic (Helmholtz coils) that produces the static magnetic field of 4.5 mT. The transmitter and the receiver were built by using available DAQ boards form National Instruments. These boards are controlled using Labview environment. The system is versatile, flexible and easy to replicate. This was actually the underlying idea behind this
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Application of SQUIDs to low temperature and high magnetic field measurements—ultra low noise torque magnetometry

Application of SQUIDs to low temperature and high magnetic field measurements—ultra low noise torque magnetometry

fixed on a PRC400 micro-cantilever and installed on our cryostat (see inset of Fig. 1). Its magnetic torque was measured at a temperature of (700 ± 20) mK in mag- netic fields up to 15 T. Data were taken during mag- netic field down sweeps at a constant rate of 30 mT/min. During a magnetic field sweep from 15 to 7.5T, i.e. in approximately four hours, we detect on the order of hun- dred flux jumps and on the order of ten integrator resets of our SQUID, showing the long term stability of the FLL. Whilst flux-jumps equilibrate on a time scale much shorter than our excitation frequencies and do not cause signal disturbances, integrator resets usually cause spikes in our lock-in signal. Most of these events can be traced back to broadband pulses in the main electrical power
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A flexible nanobrush pad for the chemical mechanical planarization of Cu/ultra low к materials

A flexible nanobrush pad for the chemical mechanical planarization of Cu/ultra low к materials

With the development of semiconductor industry, the fea- ture size of device is scaling down, and the density of inte- grated circuit (IC) is continuously increasing, as well as the wafer sizes. As a result, the fabrication techniques are facing new challenges. For instance, the conventional silica is replaced by ultra-low-к materials integrating with copper (Cu) for reduction of the dielectric permittivity [1]. Chem- ical mechanical planarization (CMP), which is thought as the only one that can offer excellent local and global planar- ization at the same time, has become one of the most im- portant fabrication technologies adopted by the semiconductor industry [2]. However, due to low density, poor mechanical strength, and deficient adhesion proper- ties, ultra-low-к dielectrics may be damaged by stresses ap- plied during the conventional CMP [3]. The pace of incorporating advanced ultra-low-к materials has been slowing down as compared to the original projections [1,4]. One solution is to reduce down pressure in the CMP process [5]. However, the low down pressure leads to a low material removal rate (MRR) in the CMP process with con- ventional polishing slurries and pads [6]. Therefore, it is an
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Dual-Band UHF RFID Tag Antenna Using Two Eccentric Circular Rings

Dual-Band UHF RFID Tag Antenna Using Two Eccentric Circular Rings

In this paper, a new low profile UHF RFID dual-band tag antenna consisting of two eccentric circular rings with a short-circuited arc-shaped feeding strip in between is presented. The outer ring resonates at 866 MHz, and the inner ring resonates at 956 MHz (catering to the RFID bands used in Europe and Japan respectively), hence providing dual-band response. The two rings are simultaneously excited by the arc-shaped feeding strip with the IC chip using microstrip-line coupling method [16]. The input impedance of conventional microstrip antennas is usually designed to match the 50 Ω impedance of the traditional feeder. However, in UHF RFID tags, the microchips have capacitive input impedance. Therefore, to enable maximum power transfer, the tag antenna must be designed to have inductive impedance for conjugate matching. The proposed antenna uses the commercially available Impinj Monza 4 tag chip (threshold power P th = − 17 . 4 dBm), which has impedances of 13 − j 151Ω at 866 MHz
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Influence of alternating low frequency magnetic field on improvement of seed quality

Influence of alternating low frequency magnetic field on improvement of seed quality

The main goal of agriculture is the production of appropriate foods quantities with a specific qualitative cha- racter. To achieve this goal, many things are needed for pro- duction. One method which improves a crop is fertilization. But this method is expensive and causes adverse effects on the environment. Therefore people strive to use those kinds of methods which are safe for the natural environment. Plants are exposed to physical stimuli, for example: infrared radiation, ultraviolet radiation, ionizing radiation, ultra- sounds and magnetic fields (Bochniak and Weso³owska- Janczarek, 2005; Carbonell et al., 2000).
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Near field scanning and propagation of correlated low frequency radiated emissions

Near field scanning and propagation of correlated low frequency radiated emissions

Abstract—Electromagnetic radiation from complex printed circuit boards can occur over a broad frequency bandwidth, ranging from hundreds of MHz to tens of GHz. This is becoming a critical issue for assessment of EMC and interoperability as electronic components become more and more integrated. We use emissions from an enclosure with a single-slot aperture and equipped with operating electronics to exemplify and model such sources. Spatial correlation functions obtained from two-probe measurements are used both to characterise the source and to propagate the emissions. We examine emissions in the sub- microwave frequency range, where evanescent decay dominates the measured correlation function at the distances measured. We find that an approximate, diffusion-like propagator describes the measured emissions well. A phase-space approach based on Wigner functions is exploited to develop this approximation and to provide enhanced understanding of the emissions.
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The Development of Ultra Thin Speakers for Mobile Phones

The Development of Ultra Thin Speakers for Mobile Phones

Figure 12 Correlation between structural factors The feature of the piezoelectric speaker in the elas- tic supporting structure is that the fundamental reso- nant frequency is greatly affected by the film shape. In conventional piezoelectric speakers, it was neces- sary to change the shape of the piezoelectric ceram- ics and the shape of the shim material to control the fundamental resonance frequency, causing problem- atic design restrictions. However, in an elastic sup- porting structure, the characteristic can be controlled simply by changing the film thickness, creating a greater degree of design freedom.
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Field trials of proposed procedure for the assessment of low frequency noise complaints

Field trials of proposed procedure for the assessment of low frequency noise complaints

In four out of the six field trials the EHO could find no environmental noise consistent with the complaint (which is a fairly typical ratio). Such cases frequently remain open for extended periods, although if no environmental noise can be found there is no real possibility of remedial action by the EHO. The results of the field trials indicate that the procedure could provide a useful tool to help close such cases. From the EHOs perspective this is positive because they will not need to spend time and resources when there is no action they can take to improve the situation. We would argue that this is also positive from the complainant’s point of view, because if no environmental noise can be identified there is nothing to be gained from further EHO involvement. However, this line of argument will only be fully effective when there are realistic alternative options available. Consequently, we would recommend (as was also recommended in [Le03] and [Mo05a] as well as other places) that further research be conducted into understanding the causes of the complaints, as well into ways of relieving the symptoms, such as ‘relief strategies’.
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Effect of electromagnetic field of extremely low frequency on ATPase activity of actomyosin

Effect of electromagnetic field of extremely low frequency on ATPase activity of actomyosin

activity of rabbit skeletal muscle was evaluated by the Fiske­Subbarow method during a five­hour exposition of protein solutions in electromagnetic field of extremely low frequency of 8 Hz and 25 µT induction. The results of the study of the ATPase activity of actomyosin upon electromagnetic expo­ sure have shown statistically significant changes that are characterized by a rather complex time dynamics. After 1, 2 and 4 hours of exposure of protein solutions the effect of ELF EMF exposure inhibits the ATPase activity compared to control samples, which are not exposed to the magnetic field. By the third and fifth hours of exposure to the electromagnetic field, there is a significant increase in the ATPase activity of actomyosin. It should be noted that a similar pattern of change in enzyme activity was universal, both for the en­ vironment by Mg 2+ and Ca 2+ , and in the absence
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User-Controlled Low Power Home Surveillance System

User-Controlled Low Power Home Surveillance System

In order to reduce the power consumption, the alert sensor group uses PIR sensors and pressure sensors.PIR is basically made of pyroelectric sensors to develop an electric signal in response to a change in the incident thermal radiation. Every living body emits some low level radiations and the hotter the body, the more is emitted radiation [9]. Commercial PIR sensors typically include two IR-sensitive elements with opposite polarization. When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or an animal passes by, it first intercepts one half of the PIR sensor which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected. Figure 3 shows the output waveform the PIR sensor [3]. In order to shape the field of view of the sensor and to cover much larger area, Fresnel lens is used. Along with pyroelectric sensor, a PIR sensing IC has been used to produce the digital output. But the PIR sensor cannot sense a low speed or heat-insulated object.
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Remote Plasma Maintenance in Low Pressure Discharges with an External Magnetic Field

Remote Plasma Maintenance in Low Pressure Discharges with an External Magnetic Field

The construction of the rf sources for plasma processing technology [1-3] has brought to the fore the nonlocality of the discharge behavior and the mechanisms of the re- mote plasma maintenance. Concerning hydrogen dis- charges, the rf source of negative hydrogen ion beams [4] developed for the neutral-beam-injection plasma heating in the international tokamak ITER is a particular case of such type of a discharge. Since the source is a two- chamber one with rf power deposition to the first cham- ber and plasma expansion in the second—bigger size— chamber, effects of nonlocality, i.e. the fluxes (charged- particle and electron-energy fluxes), govern its operation [5]. Moreover, with its design of a tandem source with a magnetic filter located in the second chamber, the plasma expanding from the first chamber passes through a region with a magnetic field. In a way, the description of the source operation provides a possibility for studying com- bined effects of nonlocal discharge behavior both without and with an external magnetic field, as it is done here.
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