Peak Vacuum Research Articles

Global solar photospheric and coronal magnetic field over activity cycles 21–25

The evolution of the global solar magnetic field from the beginning of cycle 21 (mid-1970s) until the currently-ascending cycle 25 is described using photospheric full-disk and synoptic magnetograms from NSO Kitt Peak Vacuum Telescope (KPVT) 512-channel and Spectromagnetograph (SPMG) and the Synoptic Optical Long-term Investigation of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) and Global Oscillations Network Group (GONG), and Stanford University’s Wilcox Solar Observatory (WSO). The evolving strength and symmetry of the global coronal field are described by potential-field source-surface models decomposed into axisymmetric and non-axisymmetric, and even- and odd-ordered magnetic multipoles. The overall weakness of the global solar magnetic field since cycle 23 splits the 50-year observing window into the stronger, simpler, more hemispherically symmetric cycles 21 and 22 and the weaker, more complex cycles 23 and 24. An anomalously large decrease in the global solar field strength occurred during cycles 23, and an anomalously weak axial/polar field resulted from that cycle, accompanied by an anomalously weak radial interplanetary magnetic field (IMF) during cycle 23 activity minimum and a weakened radial IMF overall since cycle 23. The general long-term decline in solar field strength and the development during cycle 24 of strong swings of hemispheric and polar asymmetry are analyzed in detail, including their transfer through global coronal structural changes to dominate mean in situ interplanetary field measurements for several years. Although more symmetric than cycle 24, the rise phase of cycle 25 began with the southern leading the northern hemisphere, but the north has recovered to lead this cycle’s polar field reversal. The mean polar flux (poleward of ±60°) has reversed at each pole, so far more symmetrically than the cycle 23 and 24 polar reversals.

The effect of various automatic cluster removal switch-point settings on milking and overmilking duration and total, peak and overmilking claw vacuum in dairy cows

AbstractThis research communication describes the effect of three automatic cluster removal (ACR) switch-point settings on machine-on time, overmilking duration, and the mean, peak-flow and overmilking vacuums. The objective was to reduce the overmilking and milking time, attaining a lower mean claw vacuum during overmilking. In a randomised experiment, 25 cows were subjected to three ACR switch-point settings at flow rates of 0.840 kg/min, 0.630 kg/min and 0.504 kg/min each for 15 morning-milkings. Pre-milking preparations and cow comfort were observed and evaluated, showing evidence that the switch-point setting of 0.840 kg/ml denoted the least proportion of behavioural problems (1.1% ± 0.6) compared to the settings at 0.640 kg/ml (16.0% ± 2.2) and 0.504 kg/ml (9.4% ± 1.7). A VaDia device (Biocontrol) determined the machine-on time and vacuum levels at the claw, mouthpiece and pulsator chamber. The machine-on time varied from 290 ± 72.8 (mean ± sd) to 289 ± 64.4 and 303 ± 66.3 for the 0.840, 0.630 and 0.504 kg/min settings, respectively. Overmilking was shortened by 29.3% and 26.4% and the claw vacuum during overmilking was reduced by 3.7 kPa and 4.3 kPa when using the 0.840 kg/min switch-point setting, compared to the others. An increased cluster-removal milk flow threshold reduced both overmilking and vacuum level during overmilking, lowering the risk of teat damage. Adapting ACR switch-point settings offers a valuable opportunity to increase parlour efficiency and cow comfort in dairy herds.

Examination of Excitation Temperature of Vacuum Arc Based on Collisional-Radiative Model

The excitation temperature is a widely measured plasma parameter. In this article, the validity of an excitation temperature measurement is verified using a transition simulation between excited levels based on a collisional-radiative model. The collisional-radiative model calculation was validated by comparing it with the results of a spectroscopic measurement for a 2-kA peak vacuum arc ignited between the Cu100, Cu80Cr20, and Cu50Cr50 electrodes, whose diameter and gap length are 10 and 5 mm, respectively. As a result, the experimental result of the spectroscopy can be well simulated using the collisional-radiative model when the electron temperature and electron density are set to approximately 1.1-1.2 eV and 1.3- 2.1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , respectively. It was found that the excitation temperature can be obtained from only two lines (510.6- and 515.3-nm lines) of the Cu I spectra with an accuracy comparable to that obtained from many line spectra of Cu neutrals. In addition, the relaxation times of the two lines are shorter than 100 ns. The excitation temperature, the electron temperature, and the electron density of the Cu100 electrodes were slightly higher than those of Cu50Cr50 electrodes. Such dependence on electrode material is caused by the difference in the density of the neutrals and ions. A comparison of the deposition ratio of Cu and Cr on the viewing port glass measured using energy-dispersive X-ray spectroscopy and a comparison of the cathode spot number suggest that the difference in the density of the neutrals and ions is caused by the difference in the cathode spot current.

No long-term effect of oral stimulation on the intra-oral vacuum in healthy premature infants.

Exclusive breastfeeding is recommended for the first 6months of life, but the breastfeeding rate in premature infants is low. We examined the effect of oral stimulation on infant's strength of suction and the relation between this intra-oral vacuum and breastfeeding duration. Between 2016 and 2018, 211 infants in a Danish neonatal unit were randomised 1:1 and of these 108 to oral stimulation intervention and 103 to control. Suction was measured as peak vacuum at enrolment and a corrected age of 6weeks. Breastfeeding duration was registered. Vacuum increased from enrolment to a corrected age of 6weeks in all infants, and no effect of oral stimulation intervention was demonstrated P=.08. Infants born ≤32 gestational weeks had lower vacuum compared with infants born after, 350 vs 398mbar P<.001. For infants born after 32 gestational weeks, the odds ratio for exclusive breastfeeding at 6months was 1.99 per 100mbar increase in vacuum P=.01. In our study, infant's intra-oral vacuum increased with age and was not affected by the oral stimulation intervention. For infants born after 32 gestational weeks, the exclusive breastfeeding rate was positively associated with a strong vacuum.

A probabilistic assessment of PWR SNF pinching failure considering hydride-related cladding embrittlement

A probabilistic methodology to investigate pinching failure of pressurized water reactor (PWR) spent nuclear fuel (SNF) rod cladding is presented. The considered accident scenario is a 9-m SNF transportation cask drop after long-term SNF dry storage. The offset strain was used to evaluate cladding failure. A set of 3000 pinching scenarios was generated via Latin Hypercube Sampling (LHS) of geometrical, material, and loading parameters and finite element (FE) models were developed to simulate each scenario. The methodology considers hydride-related cladding embrittlement related to SNF dry storage cool-down. Regression and interpolation models were developed to estimate the cladding offset strain capacity as a function of cladding hydrogen content, peak vacuum drying cladding hoop stress, and cladding temperature at the moment of load application. The probabilistic results indicate a small likelihood of hydride-related pinching failure in the considered accident scenario, after 30 or 300 years of SNF dry storage.

Estimating Total Open Heliospheric Magnetic Flux

Over the solar-activity cycle, there are extended periods where significant discrepancies occur between the spacecraft-observed total (unsigned) open magnetic flux and that determined from coronal models. In this article, the total open heliospheric magnetic flux is computed using two different methods and then compared with results obtained from in-situ interplanetary magnetic-field observations. The first method uses two different types of photospheric magnetic-field maps as input to the Wang Sheeley Arge (WSA) model: i) traditional Carrington or diachronic maps, and ii) Air Force Data Assimilative Photospheric Flux Transport model synchronic maps. The second method uses observationally derived helium and extreme-ultraviolet coronal-hole maps overlaid on the same magnetic-field maps in order to compute total open magnetic flux. The diachronic and synchronic maps are both constructed using magnetograms from the same source, namely the National Solar Observatory Kitt Peak Vacuum Telescope and Vector Spectromagnetograph. The results of this work show that the total open flux obtained from observationally derived coronal holes agrees remarkably well with that derived from WSA, especially near solar minimum. This suggests that, on average, coronal models capture well the observed large-scale coronal-hole structure over most of the solar cycle. Both methods show considerable deviations from total open flux deduced from spacecraft data, especially near solar maximum, pointing to something other than poorly determined coronal-hole area specification as the source of these discrepancies.

The reversal of the Sun’s magnetic field in cycle 24

Analysis of synoptic data from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) and the NASA/NSO Spectromagnetograph (SPM) at the NSO/Kitt Peak Vacuum Telescope facility shows that the reversals of solar polar magnetic fields exhibit elements of a stochastic process, which may include the development of specific patterns of emerging magnetic flux, and the asymmetry in activity between Northern and Southern hemispheres. The presence of such irregularities makes the modeling and prediction of polar field reversals extremely hard if possible. In a classical model of solar activity cycle, the unipolar magnetic regions (UMRs) of predominantly following polarity fields are transported polewards due to meridional flows and diffusion. The UMRs gradually cancel out the polar magnetic field of the previous cycle, and rebuild the polar field of opposite polarity setting the stage for the next cycle. We show, however, that this deterministic picture can be easily altered by the developing of a strong center of activity, or by the emergence of an extremely large active region, or by a ‘strategically placed’ coronal hole. We demonstrate that the activity occurring during the current cycle 24 may be the result of this randomness in the evolution of the solar surface magnetic field.

Инверсия магнитного поля Солнца в 24-м цикле

Analysis of synoptic data from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) and the NASA/NSO Spectromagnetograph (SPM) at the NSO/Kitt Peak Vacuum Telescope facility shows that the reversals of solar polar magnetic fields exhibit ele-ments of a stochastic process, which may include the development of specific patterns of emerging magnetic flux, and the asymmetry in activity between northern and southern hemispheres. The presence of such irregu-larities makes the modeling and prediction of polar field reversals extremely hard if possible. In a classical model of solar activity cycle, the unipolar magnetic regions (UMRs) of predominantly following polarity fields are transported polewards due to meridional flows and dif-fusion. The UMRs gradually cancel out the polar mag-netic field of the previous cycle, and rebuild the polar field of opposite polarity setting the stage for the next cycle. We show, however, that this deterministic picture can be easily altered by the developing of a strong cen-ter of activity, or by the emergence of an extremely large active region, or by a ‘strategically placed’ coronal hole. We demonstrate that the activity occurring during the current cycle 24 may be the result of this random-ness in the evolution of the solar surface magnetic field.

Vacuum characteristics of the sucking cycle and relationships with milk removal from the breast in term infants

BackgroundThe importance of an infant's intra-oral vacuum in milk removal from the breast has been established. However, the relationship between the vacuum curve and milk transfer is not well understood. AimsTo investigate the parameters of the infant suck cycle in relation to the volume of milk removed from the breast. Study designCross-sectional study to elucidate the role of infant intra-oral vacuum in efficient milk removal from the breast. SubjectsNineteen fully breastfed term infants. MethodsIntra-oral vacuum was recorded during monitored breastfeeds using a pressure transducer. Ultrasound imaging (milk flow) and respiratory inductive plethysmography (swallowing) were used to determine the nutritive sucking (NS) portion of the feed. Milk intake was determined by weighing infants before and after feeds. Vacuum traces of the first and next 2min of NS from the first breast were analysed. ResultsThe volumes of milk removed during both NS periods were negatively associated with peak vacuum (p<0.001) and rate of vacuum application (p<0.001), and positively related to area under first half of the suck cycle (p<0.001). Most parameters changed significantly from the first 2min of NS to the next 2min including significant reduction in peak vacuum and area under first half of the suck cycle. ConclusionThese results further support the role of intra-oral vacuum, specifically optimal peak vacuum, in effective and efficient milk removal during breastfeeding. It also appears that infants modify their sucking dynamics to adapt to changes in milk flow during milk ejection as the breast empties.

Reconstructing solar magnetic fields from historical observations

Aims. The present work is the first in a series of articles that develop a new proxy to represent the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements.Methods. We use synoptic (Carrington) maps from 1915–1985 that were derived from daily Ca K line observations at Mount Wilson Observatory to identify the chromospheric plages and to create synoptic pseudo-magnetograms. We use historical observations of sunspot magnetic fields from 1917 to the present to assign polarity to pixels situated within plages. The original Ca K spectroheliograms are nonuniform in their brightness, and we develop a novel approach to re-normalize their intensities.Results. We show that a homogeneous long-term series of pseudo-magnetograms can be successfully constructed by combining sunspot field measurements and plages with renormalized intensities. In our tests, about 80% of pixels situated within plages showed the same magnetic polarity as the synoptic magnetograms taken with the Kitt Peak Vacuum Telescope. Finally, we discuss possible approaches to further improve the agreement between observed and pseudo-magnetograms.

Optimizing drive parameters of a nanosecond, repetitively pulsed microdischarge high power 121.6 nm source

Utilizing nanosecond high voltage pulses to drive microdischarges (MDs) at repetition rates in the vicinity of 1 MHz previously enabled increased time-averaged power deposition, peak vacuum ultraviolet (VUV) power yield, as well as time-averaged VUV power yield. Here, various pulse widths (30–250 ns), and pulse repetition rates (100 kHz–5 MHz) are utilized, and the resulting VUV yield is reported. It was observed that the use of a 50 ns pulse width, at a repetition rate of 100 kHz, provided 62 W peak VUV power and 310 mW time-averaged VUV power, with a time-averaged VUV generation efficiency of ∼1.1%. Optimization of the driving parameters resulted in 1–2 orders of magnitude increase in peak and time-averaged power when compared to low power, dc-driven MDs.

Viscoelastic properties measurement of the prolapsed anterior vaginal wall: a patient-directed methodology

ObjectiveIn-vivo measurement of the viscoelastic properties of the prolapsed anterior vaginal wall (AVW) in post-menopausal women undergoing cystocele repair. Study designA BTC-2000™ cutometer-like instrument was introduced during vaginal repair of symptomatic stage 2–3 AVW prolapse. Under anesthesia, 10-mm orifice probe was applied to the AVW at the level of the bladder neck. A suction pressure ramp (0 to −147mmHg in 6s) was delivered causing tissue uplift, followed by immediate release to 0mmHg, measuring tissue relaxation for 20s. Similar measurements were performed over the suprapubic region (SP) for comparison purpose. The rate of tissue recovery was obtained by fitting a Voigt model to the data and expressing results as the ratio E/η [(spring modulus E)/(dashpot viscosity η)]. The effective strain energy (SE) was calculated from the pressure-uplift data and evaluated from initiation to: (1) maximum storage in tissue at peak vacuum; (2) tissue recovery after vacuum release; (3) net SE loss over the entire loading-unloading cycle. ResultsIn 22 women, higher AVW peak and residual tissue uplift values, and lower E/η ratios were found compared with SP results. The AVW stored less elastic strain energy at peak vacuum than did the SP, and AVW net energy loss over the uplift-recovery cycle was greater than for SP controls. Not only was the AVW more compliant than the SP, with higher viscous damping, but the tissue was also less able to store recoverable energy upon distension. ConclusionSuch in-vivo measurements quantify the biomechanical properties of the prolapsed AVW and may assist in its management.

Tongue movement and intra-oral vacuum of term infants during breastfeeding and feeding from an experimental teat that released milk under vacuum only

BackgroundRecent literature supports the theory that vacuum is integral to the removal of milk from the breast rather than peristaltic compression of the breast. AimWe aimed to determine if breastfed infants could remove breast milk from an experimental teat designed to release milk only when a vacuum is applied. MethodsSubmental ultrasound images and intra-oral vacuum measurements were recorded simultaneously during both a breastfeed and a feed with the experimental teat. ResultsInfants placed the nipple and teat a similar distance from the nipple hard–soft palate junction when the tongue was lowered (4.7mm vs 5.3mm). As the tongue lowered the nipple and teat expanded evenly although the nipple expanded more than the teat (3.1mm vs 1.5mm). Both baseline (−31mm Hg vs −12mm Hg) and peak vacuum (−122mm Hg vs −67mm Hg) applied to the breast were significantly higher than for the teat. ConclusionBreastfed infants are able to remove milk from a teat using only vacuum with a similar tongue movement to that of breastfeeding. This evidence supports the theory that vacuum is a critical factor in the removal of milk from the breast.

A HEMISPHERIC HELICITY SIGN RULE INDICATED BY LARGE-SCALE PHOTOSPHERIC MAGNETIC FIELDS AT THREE PHASES OF SOLAR CYCLE 23

The hemispheric sign rule of current helicity is examined for large-scale magnetic fields, extending to 60° high in solar latitudes, at three different phases of solar cycle 23 and using three different instruments. The current helicity is calculated from the vector magnetic fields derived respectively from the longitudinal full-disk magnetograms obtained by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory as well as the Kitt Peak Vacuum Telescope and the Synoptic Long-term Investigations of the Sun at the National Solar Observatory at Kitt Peak. We have used the same technique introduced by Pevtsov & Latushko to retrieve the vector magnetic field but have applied a different method to calculate the current helicity. Our analysis strengthens evidence that the large-scale magnetic fields show a clear and consistent current helicity pattern that follows the established hemispheric rule, that is, a positive helicity sign in the southern hemisphere and a negative helicity sign in the northern hemisphere. This hemispheric sign pattern is present everywhere in the global magnetic field, extending to 60° high in solar latitudes, independent of the instruments and parameters used, and is evident at both solar maximum and minimum phases.

Long-term evolution of sunspot magnetic fields

AbstractIndependent of the normal solar cycle, a decrease in the sunspot magnetic field strength has been observed using the Zeeman-split 1564.8nm Fe I spectral line at the NSO Kitt Peak McMath-Pierce telescope. Corresponding changes in sunspot brightness and the strength of molecular absorption lines were also seen. This trend was seen to continue in observations of the first sunspots of the new solar Cycle 24, and extrapolating a linear fit to this trend would lead to only half the number of spots in Cycle 24 compared to Cycle 23, and imply virtually no sunspots in Cycle 25.We examined synoptic observations from the NSO Kitt Peak Vacuum Telescope and initially (with 4000 spots) found a change in sunspot brightness which roughly agreed with the infrared observations. A more detailed examination (with 13,000 spots) of both spot brightness and line-of-sight magnetic flux reveals that the relationship of the sunspot magnetic fields with spot brightness and size remain constant during the solar cycle. There are only small temporal variations in the spot brightness, size, and line-of-sight flux seen in this larger sample. Because of the apparent disagreement between the two data sets, we discuss how the infrared spectral line provides a uniquely direct measurement of the magnetic fields in sunspots.

Laser heating of large noble gas clusters: from the resonant to the relativistic interaction regimes**© British Crown Copyright 2008/MOD

Wide-ranging measurements of sub-picosecond laser interactions with large noble gas cluster targets have been conducted in order to help clarify the nature and extent of the underlying laser–plasma heating. Within the sub-relativistic vacuum irradiance range of 1016–1017 W cm-2, we find that electron temperatures measured with continuum x-ray spectroscopy exhibit a pronounced multi-keV enhancement. Analysis indicates this behaviour to be consistent with collisional or collisionless resonant heating mechanisms. We also present the first measurements of laser-to-cluster energy deposition at relativistic vacuum irradiances, our data demonstrating absorption fractions of 90% or more. Optical probing was used to resolve the onset of a supersonic ionization front resulting from this very high absorption, and shows that despite significant pre-focus heating, the greatest plasma energy densities can be generated about the vacuum focus position. Electron energy spectra measurements confirm that laser–plasma super-heating occurs, and together with ion data establish that relativistic laser–plasma coupling in atomic clusters can take place without significant MeV particle beam production. In conjunction with optical self-emission data, the optical probing also indicates laser pre-pulse effects at peak vacuum irradiance of 5 × 1019 W cm-2. Laser absorption, plasma heating and energy transport data are supported throughout with analytical and numerical modelling.

Tongue movement and intra-oral vacuum in breastfeeding infants

The mechanism by which the breastfeeding infant removes milk from the breast is still controversial. It is unclear whether the infant uses predominantly intra-oral vacuum or a peristaltic action of the tongue to remove milk from the breast. The aim of this study was to use ultrasound to observe movements of the tongue during breastfeeding and relate these movements to both milk flow and simultaneous measurements of intra-oral vacuum. Submental ultrasound scans of the oral cavity of 20 breastfed infants (3-24 weeks old) were performed during a breastfeed. Intra-oral vacuums were measured simultaneously via a milk-filled supply line (SNS) connected to a pressure transducer. Vacuum increased during the downward motion of the posterior tongue and at the same time milk flow and milk ducts in the nipple was observed. Peak vacuum (-145+/-58 mmHg) occurred when the tongue was in the lowest position. Ultrasound imaging demonstrated that milk flow from the nipple into the infant's oral cavity coincided with both the lowering of the infants tongue and peak vacuum. Therefore vacuum is likely to play a major role in milk removal from the breast.

Solar Cycle Changes in Sunspot Umbral Intensity

The minimum intensities of sunspot umbrae were measured from 1992 through 2003 using the National Solar Observatory Kitt Peak Vacuum Telescope spectromagnetograph data. The resulting 3931 umbral measurements reveal a solar cycle variation in the umbral intensity, with umbrae appearing brighter on average at cycle minimum and darker at cycle maximum. Recent studies of umbral intensity have been in direct conflict with each other, showing decreasing, increasing, or no umbral intensity trends. By providing a longer temporal baseline, our new measurements uncover a solar cycle oscillation in umbral intensity. From this new perspective we show how previous studies agree with our work and with each other when the same phase of the solar cycle is examined. Also in agreement with other investigators, the solar cycle variation in the daily average umbral area, the lognormal distribution of umbral area, and the near constancy of the mean umbral radius during the solar cycle are seen in this data.

Numerical study of nanosecond laser interactions with micro-sized single droplets and sprays of xenon

We present a thorough numerical study on interactions of a nanosecond laser with micro-sized xenon droplets. We developed a code which allows simulation of laser interactions with a single droplet as well as a spray. We give a detailed description of the code, and we present results on the dynamics of a microplasma produced by irradiation of a single xenon droplet with a laser focused at peak vacuum intensity in the 5×1010−5×1012 W∕cm2 range. We find that the heating of the plasma depends dramatically on the laser parameters (duration, pulse shape, and intensity) on one hand, and on the droplet diameter on the other. We also present results obtained with a spray which show that the dynamics of the microplasmas is very sensitive to the position of the droplets in the interaction volume. The predictions of our model agree well with recent experimental observations performed on laser-produced plasma sources for extreme ultraviolet lithography. In particular, the postprocessing of our data with a sophisticated atomic physics code has allowed us to reproduce quite well the spectrum emitted in the extreme ultraviolet range by a xenon plasma generated by laser irradiation of a spray of droplets.

Investigation of long-duration arcade flares

Aims. We present the analysis of the three well-observed long-duration arcade flares (LDAFs). We aim to find general properties of LDAFs. In this paper results concerning morphology and physical parameters in these flares are shown. Methods. Yohkoh observations, Kitt Peak Vacuum Telescope (KPVT) magnetograms and GOES /SEM measurements are used to determine morphology and evolution of the analysed flares and physical parameters of their loop-top kernels (temperature, density, altitude). Results. We found that: (1) a so-called arcade channel may exist in LDAFs; (2) the energy release in LDAFs occurs in several places simultaneously and the reconnection process is not uniform along the flaring arcade; (3) a presence of $20{-}30$ MK hot plasma during the decay phase suggests that the reconnection occurs after the LDAF maximum.