arXiv subjects

X. Y. Xu

Publications and source records attributed to X. Y. Xu.

5 recordsLinked to original sources

arXiv2026

First \textit{ab initio} calculations of first-forbidden $β$ transitions in the reactor antineutrino anomaly

Forbidden $β$ transitions are important for understanding the reactor antineutrino anomaly. Starting from chiral two- plus three-nucleon forces, we have derived the valence-space effective Hamiltonian and effective operators of first-forbidden transitions using the many-body perturbation theory. 20 dominant first-forbidden transitions have been investigated, which provide important contributors to the reactor antineutrino spectrum anomaly. Calculated $\log ft$ values are in reasonable agreement with experimental data. Obtained shape factors exhibit significant deviations from the values approximated with forbidden transitions treated as allowed transitions. The ``5 MeV bump'' observed in the experimental ${}^{235}$U-fission antineutrino spectrum was discussed with self-consistent shape factors obtained in the present \textit{ab initio} calculations. Unlike phenomenological models that require empirical quenching factors to reproduce $β$-decay data, the present \textit{ab initio} calculations do not need to introduce quenching factors for calculations of the first-forbidden transitions.

nucl-th↗

arXiv2026

Three-body Effect in Short-range Correlations

Short-range correlations (SRCs) provide the link between low- and high-energy nuclear physics and can be quantified by two-nucleon densities. We present calculations of the two-nucleon densities using free-space similarity renormalization group (SRG)-evolved operators and in-medium SRG (IMSRG) ground states with softend chiral interaction. Our calculations benchmark well against no-core shell model (NCSM) results with unevolved oparetors and Hamiltonians in $^4\mathrm{He}$. We explicitly include the induced three-body (3b) density operators for the first time which, together with the 3b Hamiltonians, provide the full 3b effects. We show pronounced 3b effects in the $^{16}\mathrm{O}$ two-nucleon densities. Combined with valence-space IMSRG (VS-IMSRG) method, we extend the calculation to the oxygen isotopic chain. This approach enables a consistent \textit{ab initio} description of low-energy properties and SRCs within one framework and offers predictions for the upcoming SRC measurements in unstable nuclei.

nucl-th↗

arXiv2014

An ECG-on-Chip for Wearable Cardiac Monitoring Devices

This paper describes a highly integrated, low power chip solution for ECG signal processing in wearable devices. The chip contains an instrumentation amplifier with programmable gain, a band-pass filter, a 12-bit SAR ADC, a novel QRS detector, 8K on-chip SRAM, and relevant control circuitry and CPU interfaces. The analog front end circuits accurately senses and digitizes the raw ECG signal, which is then filtered to extract the QRS. The sampling frequency used is 256 Hz. ECG samples are buffered locally on an asynchronous FIFO and is read out using a faster clock, as and when it is required by the host CPU via an SPI interface. The chip was designed and implemented in 0.35um standard CMOS process. The analog core operates at 1V while the digital circuits and SRAM operate at 3.3V. The chip total core area is 5.74 mm^2 and consumes 9.6uW. Small size and low power consumption make this design suitable for usage in wearable heart monitoring devices.

cs.AR↗

arXiv2014

Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots

In strongly correlated electronic systems, such as manganites, the global transport behavior depends sensitively on the spin ordering, whose alteration often requires a large external magnetic field. Here we show that the spin ordering in manganites can be easily controlled by exchange field across the interface between a ferromagnet and a manganite. By depositing isolated ferromagnetic nanodots on a manganite thin film, we find that it is possible to overcome dimensionality and strain effects to raise the metal-insulator transition (MIT) temperature by over 200 K and increase the magnetoresistance by 5000%. The MIT temperature can also be tuned by controlling the density of the magnetic nanodots which indicates that the formation process of electronic phase separation can be controlled by the presence of magnetic nanodots.

cond-mat.str-el↗

arXiv2010

Multi-seeded melt growth (MSMG) of bulk Y-Ba-Cu-O using thin-film seeds

Y-Ba-Cu-O (YBCO) and Sm-Ba-Cu-O (SmBCO) thin films have been used for the first time as heterogeneous seeds to multi-seed successfully the melt growth of bulk YBCO in a multi-seeded melt growth (MSMG) process. The use of thin film seeds, which may be prepared with highly controlled orientation (i.e. with a well-defined a-b plane and precisely known a-direction), is based on their superheating properties and reduces significantly contamination of the bulk sample by the seed material. A variety of grain boundaries were obtained by varying the angle between the seeds. Microstructural studies indicate that the extent of residual melt deposited at the grain boundary decreases with increasing grain boundary contact angle. It is established that the growth front proceeds continuously at the (110)/(110) grain boundary without trapping liquid, which leads to the formation of a clean grain boundary.

cond-mat.supr-con↗