The Sun exhibits centennial-scale activity variations and sometimes encounters grand solar minimum when solar activity becomes extremely weak and sunspots disappear for several decades. Such an ...extreme weakening of solar activity could cause severe climate, causing massive reductions in crop yields in some regions. During the past decade, the Sun's activity has tended to decline, raising concerns that the Sun might be heading for the next grand minimum. However, we still have an underdeveloped understanding of solar dynamo mechanisms and hence precise prediction of near-future solar activity is not attained. Here we show that the 11-year solar cycles were significantly lengthened before the onset of the Maunder Minimum (1645-1715 CE) based on unprecedentedly high-precision data of carbon-14 content in tree rings. It implies that flow speed in the convection zone is an essential parameter to determine long-term solar activity variations. We find that a 16 year-long cycle had occurred three solar cycles before the onset of prolonged sunspot disappearance, suggesting a longer-than-expected preparatory period for the grand minimum. As the Sun has shown a tendency of cycle lengthening since Solar Cycle 23 (1996-2008 CE), the behavior of Solar Cycle 25 can be critically important to the later solar activity.
Carbon‐14 in tree rings have suggested there had been multiple extreme solar proton events (SPEs) in the past. While the largest events such as in 774–775 CE can be significantly detected by the ...typical precision of accelerator mass spectrometry, smaller but possibly more frequent events have been difficult to be detected. Thus, the frequency or any characteristics of such relatively smaller events are still largely unknown. In this paper, we report that large SPEs had occurred in 1261–1262, 1268–1269, and 1279–1280 CE before the onset of the Wolf minimum based on high‐precision carbon‐14 analyses. It is suggested that they had occurred at the maximum and the declining phase of solar cycles, and that they had occurred during the transition time of solar activity into a deep minimum. We propose that this episode may provide a unique opportunity to elucidate a potential interaction between the solar dynamo and extreme solar flares.
Plain Language Summary
The Sun is a magnetically active star and occasionally cause intense bursts that sometimes accompany the ejection of energetic protons, described as the solar proton events. In this paper, we report that there were three intense solar proton events in the thirteenth century, just before the onset of the Wolf grand minimum. We propose that these events may be related to the weakening of solar activity during that time.
Key Points
Multiple abrupt increases in carbon‐14 content were found during the transition time of solar activity into the grand minimum state
They occurred at solar activity maximum or at the declining phase of solar cycles, suggesting that they originate from solar proton events
The Wolf minimum may provide a unique opportunity to potentially deepen the understanding of the solar dynamo
In 2009, Yamagata University installed a compact 14C accelerator mass spectrometry (YU-AMS) system and an automated graphitization line. The YU-AMS system is based on a 0.5 MV pelletron accelerator ...(1.5SDH-1) developed by National Electrostatics Corporation (NEC). A second automated graphitization line and an additional ion source of the YU-AMS system were installed in 2014. Approximately 2,000 samples have been measured per year using the system since 2010. The long-term stability of the system from 2010 to 2021 was assessed by measuring the IAEA-C6 and IAEA-C7 standard samples graphitized by the automated graphitization line.
Abstract Objective The regulatory mechanisms responsible for acute exercise-induced expression of monocarboxylate transporters MCT1 and MCT4 mRNA in skeletal muscle remain unclear. ...5′-adenosine-activated protein kinase (AMPK) is a key signaling molecule that regulates gene expression at the mRNA level. We examined whether AMPK activation is involved in acute exercise-induced expression of MCT1 and MCT4 mRNA in fast-twitch muscle. Materials/Methods Male Sprague–Dawley rats were subjected to an acute bout of either 5 min high-intensity intermittent swimming (HIS) or 6-h low-intensity prolonged swimming (LIS). The effects of acute exercise on the phosphorylation of AMPK (p-AMPK), calcium/calmodulin pendent kinase II (p-CaMKII), p38 mitogen-activated protein kinase (p-p38MAPK), and MCTs mRNA were analyzed in vivo. To observe the direct effects of AMPK activation on MCTs mRNA, the effects of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), caffeine, and dantrolene were analyzed in vitro using an isolated muscle incubation model. Results The p-AMPK increased in response to both HIS and LIS, although the p-CaMKII and p-p38MAPK were increased only following HIS. Irrespective of exercise intensity, MCT1 and MCT4 mRNA was also transiently upregulated by both HIS and LIS. Direct exposure of the epitrochlearis muscle to 0.5 mmol/L AICAR or 1 mmol/L caffeine, which activated p-AMPK increased both MCT1 and MCT4 mRNA levels. When pAMPK was inhibited by dantrolene, neither MCT1 nor MCT4 mRNA was increased. Conclusion These results suggest that acute exercise-induced increases in MCT1 and MCT4 mRNA expression may be possibly mediated by AMPK activation, at least in part in fast-twitch muscle.
Proxy-based observations of solar activity in the past have revealed long-term variations, such as the Gleissberg cycle (~88 yr), de Vries cycle (~200 yr), and the Hallstatt cycle (~2000 yr). Such ...long-term variations of solar activity sometimes cause the disappearance of sunspots for several decades. Currently, solar activity is becoming weaker, and there is a possibility that another long-term sunspot minimum could occur. However, the detailed mechanism of the weakening in solar activity is unknown, and the prediction of solar activity is ambiguous. In this study, we investigate the transitions of solar cycle length before the onset of the Spoerer Minimum, the longest grand minimum in the past 2000 yr. We measured the 14C content in an asunaro tree (Thujopsis dolabrata) excavated at Shimokita Peninsula from 1368–1420 CE using the compact AMS system at Yamagata University. It is found that the solar cycle lengthened to be 14–16 yr from 2 cycles before the onset of the Spoerer Minimum.
Cosmogenic nuclides such as
14
C from tree rings and
10
Be and
36
Cl from ice cores are excellent proxies for the past extremely large solar energetic particle (SEP) events, which are dozens of times ...larger than the largest SEP event in the history of observation. So far, several rapid
14
C increases have been discovered, which are considered to have originated from extreme SEP events (or set of successive SEP events) from verifications using multiple cosmogenic nuclide analyses in natural archives. Although these events are characterized by a rapid increase in cosmogenic nuclide concentrations,
14
C data recorded worldwide do not always show similar variations, especially during the 993 CE event, where a rapid increase was recorded in either 992–993 CE or 993–994 CE in several records. We present new
14
C data of the Japanese cedar sample for the 993 CE event. Although the latest data show no significant increase in 1 year, an overall increase pattern is consistent with the previously reported
14
C data of the Japanese cedar, which supports that a significant
14
C increase occurred from 993 to 994 CE in the Japanese sample. Given the dominant
14
C production in high latitudes by SEPs, the difference in timing of increase may be a transport effect in the atmosphere. Moreover, the difference in the timing of the
14
C increase can cause a 1-year age-determination error using the 993 CE radiocarbon spike. Compared with the
14
C data between tree samples from high latitude and midlatitude, including Japan, high-latitude data can capture
14
C changes originating from SEP events more quickly and clearly and may be more suitable for a SEP event exploration in the past.
Status of the AMS system at Yamagata University Moriya, Toru; Takeyama, Mirei; Sakurai, Hirohisa ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
01/2019, Letnik:
439
Journal Article
Recenzirano
An accelerator mass spectrometry (AMS) system and an automated graphitization line were installed at Yamagata University (YU) in 2009. Approximately 2000 samples are measured per year using the ...YU-AMS system. The long-term stability of the system was assessed by measuring the standard sample IAEA-C7 graphitized by the automated graphitization line. In March 2014, a second automated graphitization line and an additional ion source for the YU-AMS system were installed to meet the requirement of 14C measurement for pharmacological and medical applications. A phosphoric acid treatment system was also developed for the radiocarbon dating of calcium carbonate (CaCO3) in shell and coral samples. Performance tests on the new YU-AMS system were carried out by measuring the C-series standard samples (C1-C9) and oxalic acid II (HOxII) obtained from IAEA and NIST, respectively. The results of the 14C concentration pMC are in good agreement with the consensus values. Performance tests for medical applications were also carried out by measuring the 14C concentration of 14C-glucose in human plasma.
Atmospheric radiocarbon (14C) levels increased from 1955 to 1963 due to atmospheric nuclear weapon tests, and then decreased. As 14C accumulates in human tooth enamel while the enamel is being ...formed, 14C can be used to estimate the birth year of unidentified bodies. Measurement results of 14C content in tooth enamel using accelerator mass spectrometry vary depending on the enamel's sample site. To address this problem, a method for equalizing samples using a pulverizer was considered in this study. Regarding the tube and cone used as the pulverizer, (1) a polycarbonate tube and stainless steel cone, (2) a stainless steel tube and cone, and (3) a tungsten carbide tube and cone, were compared. In (1), the modern carbon ratio was approximately half that of the normal ratio of 100 pMC, with which accurate dating was impossible, and in (2), a high background value was obtained for IAEA-C1, which was pulverized using a reusable tube and cone. In (3), the 14C content for IAEA-C1 pulverized using reusable tube and cone, which was washed with quartz sand, was 0.31 ± 0.01 pMC. This result did not show any problems regarding background value. Therefore, the use of tungsten carbide products and washing with quartz sand is recommended for 14C measurement of pulverized teeth.
•Atmospheric radiocarbon (14C) levels increased from 1955 to 1963, and then decreased.•14C analysis of human tooth enamel is useful for estimation of birth year.•14C content in enamel varies depending on the enamel's site.•To equalize samples, enamel pulverization methods were considered in this study.•When using a pulverizer, tungsten carbide products and quartz sand are recommended.
Development of pixelated silicon detector for AMS study Tokanai, Fuyuki; Moriya, Toru; Takeyama, Mirei ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
July 2024, 2024-07-00, Letnik:
552
Journal Article
Recenzirano
A pixelated silicon detector (PSD) has been developed for the position-sensitive detector on a focal plane of an accelerator mass spectrometry (AMS) system in Yamagata University (YU). The YU-AMS ...system measures the relative abundances of the carbon isotopes 14C, 13C, and 12C for radiocarbon dating. The beam of the rare isotope 14C is transported to the focal plane of the AMS system. When the focal plane detector is position-sensitive to the beam, it can be utilized for beam diagnostics on the AMS beamline to achieve 14C measurement with high accuracy. To investigate the characteristics of the PSD, α particles from 241Am were irradiated on the PSD. A beam test using 14C was also performed to evaluate the size and position of the 14C beam on the focal plane of the YU-AMS system.
Abstract
Silicon-based solid-state detectors (SSDs) are crucial for investigating the properties of superheavy elements (SHEs), since they measure the energy of SHEs and charged particles that are ...emitted as successive decay events of the SHEs. We have developed a segmented SSD for SHE studies using the new gas-filled recoil ion separators (GARIS-II and GARIS-III) at RIKEN. It is based on a back-illuminated Si PIN photodiode in which the irradiation is through the N
+
layer. The detector is introduced as a side one for the GARIS focal plane detection system. To investigate the characteristics of the SSD,
241
Am
α
particles were irradiated by automatically moving and rotating the
α
source for each segmented portion of the SSD. A Monte Carlo simulation was also performed to estimate the dead layer thickness of the segmented SSD.
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