New criteria for selecting reliable Thellier-type paleointensity results from the 1960 Kilauea lava flows, Hawaii

Thellier-type paleointensity experiments associated with partial thermal remanent magnetization checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies have revealed that a substantial portion of paleointensity results with positive checks for historical lava samples largely fails to predict known Earth magnetic field intensity values. To determine the fidelity of paleointensity values, conventional Thellier-type paleointensity experiments were performed on Kilauea lava flows that erupted in 1960. The positive partial thermal remanent magnetization checks for our results range from 30.28 ± 1.38 µT to 52.94 ± 1.89 µT. This strongly indicates that conventional paleointensity checks cannot guarantee the fidelity of paleointensity results, especially when the unblocking temperatures for the newly formed magnetic particles are higher than the treatment temperature. Therefore, in this study, to check for thermal alteration during heating, the temperature dependence of the hysteresis parameter measured at room temperature for the thermally treated samples was also measured. Our new results show that nearly all biased paleointensity values correspond to a ratio of the coercivity of remanence to the magnetic coercivity of > 3 and a chemical alteration index > ~ 10%, which indicates the strong effect of the domain state and thermal alteration on the fidelity of the paleointensity results. Our study provides feasible criteria to further improve the fidelity of paleointensity estimations.

New Criteria for Selecting Reliable Thellier-Thellier type Paleointensity Results from the 1960 Kilauea Lava Flow, Hawaii

Thellier-Thellier type paleointensity experiments associated with partial thermal remanent magnetization (pTRM) checks have been widely used to determine paleointensity values from volcanic and archaeological media. However, previous studies further revealed that a substantial portion of paleointensity results with positive checks for historical lavas largely fails to predict the known Earth’s field intensity values. To determine the fidelity of paleointesnity values, conventional Thellier-Thellier type paleointensity experiments have been performed from the Kilauea lava flows erupted in 1960. Our results show that positive pTRM checks range from 30.34±1.39 to 53.04±1.80 μT. This strongly indicates that positive pTRM checks can’t guarantee the fidelity of paleointensity results especially when the unblocking temperatures for the newly-formed magnetic particles are higher than the treated temperature. Thus, in this study, to check thermal alteration during heating, the temperature-dependent of hysteresis parameter measured at the room-temperature for the thermally-treated samples were also measured. Our new results show that almost all biased paleointensity values correspond to Bcr /Bc >3 and CI >~10%, which indicates strong effects of domain state and thermal alteration on the fidelity of paleointensity results. Our study provides a feasible criteria to further improve the fidelity of paleointensity estimations.

DESIGN OF A 65 NM CMOS COMPARATOR WITH HYSTERESIS / 65 NM KMOP TECHNOLOGIJOS HISTEREZINIO KOMPARATORIAUS PROJEKTAVIMAS

The comparator can be described as one of the basic building blocks in electronics. It is implemented both as a discrete device and as a constituent of a complex circuit. In both cases, the circuits usually operate in conditions, where useful and unwanted (noise) signals are present at the same time. In order to maintain the validity of output data, a hysteresis parameter is introduced to the comparator’s circuit. This article presents the results of a CMOS comparator with hysteresis design – the schematic, topology and simulation results are analyzed. The designed comparator is implemented in a zero voltage offset compensation circuit ADC in a multi-standard transceiver IC. Komparatorius yra vienas iš pagrindinių elektronikos įtaisų. Jis yra naudojamas kaip diskretinis elementas arba kaip viena iš sudėtingesnės sistemos sudedamųjų dalių. Šie įtaisai dažnai veikia elektronikos sistemose, kuriose egzistuoja ne tik informaciją nešantys bei apdorojami signalai, bet ir nepageidautini triukšmo signalai. Siekiant tokiomis sąlygomis užtikrinti patikimą ir efektyvią komparatoriaus veiką, imama taikyti histerezė. Šiame straipsnyje pateikiami TSMC 65 nm KMOP histerezinio komparatoriaus projektavimo rezultatai: aptariama principinė elektrinė schema, pateikiama suprojektuota topologija, jos kompiuterinio modeliavimo rezultatai bei išvados. Šis komparatorius bus naudojamas daugiastandarčio, daugiakanalio siųstuvo-imtuvo grandinėje, nulinio potencialo poslinkio įtampą nustatančiame, lygiagrečios architektūros analoginiame skaitmeniniame keitiklyje (ASK).

Magnetic characteristics and archeointensity determination on Mesoamerican Pre-Columbian Pottery from Quiahuiztlan, Veracruz, Mexico

We report a detailed archeomagnetic investigation on pre-Columbian potteries from Quiahuiztlan, Veracruz, from ~900 AD to 1521 AD. Archeological samples analyzed by modern magnetic techniques carry a stable univectorial thermoremanent magnetization under alternating field treatment. Continuous low-field susceptibility vs. temperature curves performed in air indicates Ti-poor titanomagnetites as magnetization carriers. Few samples, however, show two ferrimagnetic phases with Curie temperatures compatible with both Ti-poor and Ti-rich titanomagnetites. Hysteresis parameter ratios fall essentially in the pseudo-single-domain region, which may indicate a mixture of multi-domain and a significant amount of single domain grains. Early geomagnetic field intensity determinations using the Coe variant of Thellier method were performed on 90 selected samples. Cooling rate corrected intensity values range from 34.0 ± 1.2 to 62.2 ± 0.2 ?T. Corresponding virtual axial dipole moments (VADM) range from 5.7 to 10.7 x1022 Am2. Absolute intensity curves for Mesoamerica present limited spa-tial/temporal resolution. For tentative dating purposes, we used global archeointensity curves reduced to central and eastern Mexico that permit preliminary dating of Quiahuiztlan potteries. Comparison of our data against those reported in ArcheoInt database allow to identify two periods 900- 1000 and 1400-1600 AD as the most probable manufacturing ranges for the pot- teries studied.