Yixuan Li - Academia.edu (original) (raw)

Papers by Yixuan Li

PLoS ONE, 2014

MicroRNAs (miRNAs) are small, non-coding RNAs that negatively regulate gene expression. It has be... more MicroRNAs (miRNAs) are small, non-coding RNAs that negatively regulate gene expression. It has been reported that miRNAs are involved in host-virus interaction, but evidence that cellular miRNAs promote virus replication has been limited. Here, we found that miR-23a promoted the replication of human herpes simplex virus type 1 (HSV-1) in HeLa cells, as demonstrated by a plaque-formation assay and quantitative real-time PCR. Furthermore, interferon regulatory factor 1 (IRF1), an innate antiviral molecule, is targeted by miR-23a to facilitate viral replication. MiR-23a binds to the 39UTR of IRF1 and down-regulates its expression. Suppression of IRF1 expression reduced RSAD2 gene expression, augmenting HSV-1 replication. Ectopic expression of IRF1 abrogated the promotion of HSV-1 replication induced by miR-23a. Notably, IRF1 contributes to innate antiviral immunity by binding to IRF-response elements to regulate the expression of interferon-stimulated genes (ISGs) and apoptosis, revealing a complex interaction between miR-23a and HSV-1. MiR-23a thus contributes to HSV-1 replication through the regulation of the IRF1mediated antiviral signal pathway, which suggests that miR-23a may represent a promising target for antiviral treatments.

Cell Research, 2009

MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcri... more MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcriptional level, and are deeply involved in the pathogenesis of several types of cancers. To investigate whether specific miRNAs and their target genes participate in the molecular pathogenesis of laryngeal carcinoma, oligonucleotide microarrays were used to assess the differential expression profiles of microRNAs and mRNAs in laryngeal carcinoma tissues compared with normal tissues. The oncogenic miRNA, microRNA-21 (miR-21), was found to be upregulated in laryngeal carcinoma tissues. Knockdown of miR-21 by specific antisense oligonucleotides inhibited the proliferation potential of HEp-2 cells, whereas overexpression of miR-21 elevated growth activity of the cells, as detected by the colony formation assay. The cell number reduction caused by miR-21 inhibition was due to the loss of control of the G1-S phase transition, instead of a noticeable increase in apoptosis. Subsequently, a new target gene of miR-21, BTG2, was found to be downregulated in laryngeal carcinoma tissues. BTG2 is known to act as a pan-cell cycle regulator and tumor suppressor. These findings indicate that aberrant expression of miR-21 may contribute to the malignant phenotype of laryngeal carcinoma by maintaining a low level of BTG2. The identification of the oncogenic miR-21 and its target gene, BTG2, in laryngeal carcinoma is potentially valuable for cancer diagnosis and therapy.

IUBMB Life, 2009

MicroRNAs are a group of endogenously expressed, singlestranded, 18-24 nt RNAs that regulate dive... more MicroRNAs are a group of endogenously expressed, singlestranded, 18-24 nt RNAs that regulate diverse cellular pathways. Although documented evidence indicates that some microRNAs can function as oncogenes or tumor-suppressors, the role of miR-214 in regulating human cervical cancer cells remains unexplored. We determined the expression level of miR-214 and found it is downregulated in cervical cancer compared with normal tissue. Overexpression of miR-214 in HeLa cells, a human cervical cancer cell line, significantly inhibited cell proliferation according to the MTT and colony forming assays. HeLa cells that stably overexpress miR-214 downregulate the expression of MEK3 and JNK1 at both mRNA and protein levels. Further investigation revealed that miR-214 regulates the expression of MEK3 and JNK1 by targeting the 3 0 UTRs of these genes. Collectively, these results suggest that miR-214 negatively regulates HeLa cell proliferation by targeting the noncoding regions of MEK3 and JNK1 mRNAs.

Clinical Nuclear Medicine, 1992

One hundred patients were studied with three-phase lung scintigraphy with Tc-99m gluconate. The r... more One hundred patients were studied with three-phase lung scintigraphy with Tc-99m gluconate. The results showed that there were statistically significant differences between benign and malignant lung lesions in the intensity of accumulation, the blood supply index ratio, and the radioactive uptake ratio. However, no difference was observed between the benign lung lesions and the healthy lungs. Analysis of false negatives and false positives revealed that false negatives had something to do with the cell types of the malignancies, in addition to the relatively small size of the lesions; the false positives were mostly caused by acute inflammation, for which obstructive pneumonitis might be responsible in part. It is concluded that Tc-99m gluconate is tumor-avid and can be used as an agent for positive imaging of lung cancer, because quantitative parameters, blood supply index ratio, and radioactive uptake ratio are more objective in distinguishing malignant lung lesions from benign ones, and are of relatively higher sensitivity and specificity. Thus, lung scintigraphy with Tc-99m gluconate provides an efficient supplementary measure for differentiating between malignant and benign lung lesions.

Cell Research, 2009

MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcri... more MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcriptional level, and are deeply involved in the pathogenesis of several types of cancers. To investigate whether specific miRNAs and their target genes participate in the molecular pathogenesis of laryngeal carcinoma, oligonucleotide microarrays were used to assess the differential expression profiles of microRNAs and mRNAs in laryngeal carcinoma tissues compared with normal tissues. The oncogenic miRNA, microRNA-21 (miR-21), was found to be upregulated in laryngeal carcinoma tissues. Knockdown of miR-21 by specific antisense oligonucleotides inhibited the proliferation potential of HEp-2 cells, whereas overexpression of miR-21 elevated growth activity of the cells, as detected by the colony formation assay. The cell number reduction caused by miR-21 inhibition was due to the loss of control of the G1-S phase transition, instead of a noticeable increase in apoptosis. Subsequently, a new target gene of miR-21, BTG2, was found to be downregulated in laryngeal carcinoma tissues. BTG2 is known to act as a pan-cell cycle regulator and tumor suppressor. These findings indicate that aberrant expression of miR-21 may contribute to the malignant phenotype of laryngeal carcinoma by maintaining a low level of BTG2. The identification of the oncogenic miR-21 and its target gene, BTG2, in laryngeal carcinoma is potentially valuable for cancer diagnosis and therapy.

Personality and Individual Differences, 2013

ABSTRACT Individuals’ development is a multilayered affair. The influence of family relationship ... more ABSTRACT Individuals’ development is a multilayered affair. The influence of family relationship on personality, such as and focusing on birth order, is subject to influence from other social systems in which the families are situated. The current research examined the relation of birth order to personality and life satisfaction in China, where only children have become the majority because of national policy. Across two studies with both between-family data (N = 1468) and within-family data (N = 171), onlyborns and laterborns surpassed firstborns on openness to experience. In addition, only-child participants were more satisfied with their own lives than were sibling participants, especially laterborns. The results offer new insights into the dynamic relations between ecology and personality.

Learning and Individual Differences, 2013

Proceedings of the International Astronomical Union, 2010

How magnetic field structure changes with eruptive events (e.g., flares and CMEs) has been a long... more How magnetic field structure changes with eruptive events (e.g., flares and CMEs) has been a long-standing problem in solar physics. Here we present the analysis of eruptionassociated changes in the magnetic inclination angle, the transverse component of magnetic field and the Lorentz force. The analysis is based on an observation of the X3.4 flare on Dec.13 2006 and a numerical simulation of a solar eruption made by Yuhong Fan. Both observation and simulation show that (1) the magnetic inclination angle in the decayed peripheral penumbra increases, while that in the central area close to flaring polarity inversion line (PIL) deceases after the flare; (2) the transverse component of magnetic field increases at the lower altitude near flaring PIL after the flare. The result suggests that the field lines at flaring neutral line turn to more horizontal near the surface, that is in agreement with the prediction of Hudson, Fisher & Welsch (2008).

Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancem... more Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancement of inner penumbrae and central umbrae after major flares. In an effort to understand the physics behind the phenomena, we study the changes of magnetic inclination angle at the peripheral and the inner penumbral regions around the time of three X-class flares, the X3.4 flare on 2006 December 13, the X2.6 flare on 2005 January 15 and the X5.3 flare on 2001 August 25. For the first event, we use the Hinode Spectro-Polarimeter (SP) vector magnetograms before and after the flare, between which there was an 8-hour interval. For the two latter events, the high cadence vector magnetograms obtained with the Digital Vector Magnetograph (DVMG) at Big Bear Solar Observatory (BBSO) are available, with which we are able to study the inclination angle as a function of time. For all the events, we find that the mean inclination angle at the penumbral decay regions increases after flares. The result suggests that penumbral fields change from a more inclined to a more vertical configuration after the flare. Furthermore, we derive the three-dimensional coronal magnetic fields using nonlinear force-free field extrapolation to study the altitude variation of magnetic inclination angle.

Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancem... more Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancement of inner penumbrae and central umbrae after major flares. In an effort to understand the physics behind the phenomena, we study the changes of magnetic inclination angle at the peripheral and the inner penumbral regions around the time of three X-class flares, the X3.4 flare on 2006 December 13, the X2.6 flare on 2005 January 15 and the X5.3 flare on 2001 August 25. For all the events, we find that the mean inclination angle at the penumbral decay regions increases after the flares. The result suggests that penumbral fields change from a more inclined to a more vertical configuration after the flare. Furthermore, we quantitatively compare our observations with recent MHD simulations of eruption, by Yuhong Fan which shows the evidence of field lines turn to more horizontal near the surface, immediately following the eruption.

Astrophysical Journal, 2011

It has been a long-standing question in solar physics how magnetic field structure changes with e... more It has been a long-standing question in solar physics how magnetic field structure changes with eruptive events (e.g., flares and coronal mass ejections). In this Letter, we present the eruption-associated changes in the magnetic inclination angle, the horizontal component of magnetic field vectors, and the Lorentz force. The analysis is based on the observation of the X3.4 flare on 2006 December 13 and in comparison to the numerical simulation of Fan. Both observation and simulation show that (1) the magnetic inclination angle in the decayed peripheral penumbra increases, while that in the central area close to the flaring polarity inversion line (PIL) deceases after the flare; (2) the horizontal component of magnetic field increases at the lower altitude near the flaring PIL after the flare. The result suggests that the field lines at the flaring neutral line turn to more horizontal near the surface, that is in agreement with the prediction of Hudson et al.

Astrophysical Journal, 2009

The Letter takes up a question of what radio emission is produced by electrons at the very accele... more The Letter takes up a question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that the radio emission from the acceleration sites: (i) has sufficiently strong intensity to be observed by currently available radio instruments and (ii) has spectra and light curves which are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.

New Astronomy, 2011

We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using m... more We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by , where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed.

The Astrophysical Journal, 2009

The Letter takes up a question of what radio emission is produced by electrons at the very accele... more The Letter takes up a question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that the radio emission from the acceleration sites: (i) has sufficiently strong intensity to be observed by currently available radio instruments and (ii) has spectra and light curves which are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.

New Astronomy, 2011

We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using m... more We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by , where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed.

Science China-physics Mechanics & Astronomy, 2009

Recent studies showed a consistent pattern of changes in the sunspot structure associated with ma... more Recent studies showed a consistent pattern of changes in the sunspot structure associated with major flares: part of the peripheral penumbral regions vanishes during flares, and meanwhile, the umbral cores and/or inner penumbral regions are darkened. To understand the underlying physics of these observations, we compare the magnetic inclination angle in the decayed peripheral and the enhanced inner penumbral regions before and after the 4B/X3.4 flare of 2006 December 13 by using the high-resolution vector magnetograms from Hinode. We find that the mean inclination angle in the decayed penumbra increases after the flare while that in the enhanced penumbra near flaring neutral line decreases. The result confirms the previous idea that two components of a δ sunspot become connected after flares. As a result of new connection, peripheral penumbral fields change from a more inclined to a more vertical configuration and transverse fields in umbral core and inner penumbral regions increase substantially (Liu et al. 2005). The flare-associated changes of Doppler width as well as other parameters (the transverse field strength, continuum intensity and filling factor) are also presented.

PLoS ONE, 2014

MicroRNAs (miRNAs) are small, non-coding RNAs that negatively regulate gene expression. It has be... more MicroRNAs (miRNAs) are small, non-coding RNAs that negatively regulate gene expression. It has been reported that miRNAs are involved in host-virus interaction, but evidence that cellular miRNAs promote virus replication has been limited. Here, we found that miR-23a promoted the replication of human herpes simplex virus type 1 (HSV-1) in HeLa cells, as demonstrated by a plaque-formation assay and quantitative real-time PCR. Furthermore, interferon regulatory factor 1 (IRF1), an innate antiviral molecule, is targeted by miR-23a to facilitate viral replication. MiR-23a binds to the 39UTR of IRF1 and down-regulates its expression. Suppression of IRF1 expression reduced RSAD2 gene expression, augmenting HSV-1 replication. Ectopic expression of IRF1 abrogated the promotion of HSV-1 replication induced by miR-23a. Notably, IRF1 contributes to innate antiviral immunity by binding to IRF-response elements to regulate the expression of interferon-stimulated genes (ISGs) and apoptosis, revealing a complex interaction between miR-23a and HSV-1. MiR-23a thus contributes to HSV-1 replication through the regulation of the IRF1mediated antiviral signal pathway, which suggests that miR-23a may represent a promising target for antiviral treatments.

Cell Research, 2009

MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcri... more MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcriptional level, and are deeply involved in the pathogenesis of several types of cancers. To investigate whether specific miRNAs and their target genes participate in the molecular pathogenesis of laryngeal carcinoma, oligonucleotide microarrays were used to assess the differential expression profiles of microRNAs and mRNAs in laryngeal carcinoma tissues compared with normal tissues. The oncogenic miRNA, microRNA-21 (miR-21), was found to be upregulated in laryngeal carcinoma tissues. Knockdown of miR-21 by specific antisense oligonucleotides inhibited the proliferation potential of HEp-2 cells, whereas overexpression of miR-21 elevated growth activity of the cells, as detected by the colony formation assay. The cell number reduction caused by miR-21 inhibition was due to the loss of control of the G1-S phase transition, instead of a noticeable increase in apoptosis. Subsequently, a new target gene of miR-21, BTG2, was found to be downregulated in laryngeal carcinoma tissues. BTG2 is known to act as a pan-cell cycle regulator and tumor suppressor. These findings indicate that aberrant expression of miR-21 may contribute to the malignant phenotype of laryngeal carcinoma by maintaining a low level of BTG2. The identification of the oncogenic miR-21 and its target gene, BTG2, in laryngeal carcinoma is potentially valuable for cancer diagnosis and therapy.

IUBMB Life, 2009

MicroRNAs are a group of endogenously expressed, singlestranded, 18-24 nt RNAs that regulate dive... more MicroRNAs are a group of endogenously expressed, singlestranded, 18-24 nt RNAs that regulate diverse cellular pathways. Although documented evidence indicates that some microRNAs can function as oncogenes or tumor-suppressors, the role of miR-214 in regulating human cervical cancer cells remains unexplored. We determined the expression level of miR-214 and found it is downregulated in cervical cancer compared with normal tissue. Overexpression of miR-214 in HeLa cells, a human cervical cancer cell line, significantly inhibited cell proliferation according to the MTT and colony forming assays. HeLa cells that stably overexpress miR-214 downregulate the expression of MEK3 and JNK1 at both mRNA and protein levels. Further investigation revealed that miR-214 regulates the expression of MEK3 and JNK1 by targeting the 3 0 UTRs of these genes. Collectively, these results suggest that miR-214 negatively regulates HeLa cell proliferation by targeting the noncoding regions of MEK3 and JNK1 mRNAs.

Clinical Nuclear Medicine, 1992

One hundred patients were studied with three-phase lung scintigraphy with Tc-99m gluconate. The r... more One hundred patients were studied with three-phase lung scintigraphy with Tc-99m gluconate. The results showed that there were statistically significant differences between benign and malignant lung lesions in the intensity of accumulation, the blood supply index ratio, and the radioactive uptake ratio. However, no difference was observed between the benign lung lesions and the healthy lungs. Analysis of false negatives and false positives revealed that false negatives had something to do with the cell types of the malignancies, in addition to the relatively small size of the lesions; the false positives were mostly caused by acute inflammation, for which obstructive pneumonitis might be responsible in part. It is concluded that Tc-99m gluconate is tumor-avid and can be used as an agent for positive imaging of lung cancer, because quantitative parameters, blood supply index ratio, and radioactive uptake ratio are more objective in distinguishing malignant lung lesions from benign ones, and are of relatively higher sensitivity and specificity. Thus, lung scintigraphy with Tc-99m gluconate provides an efficient supplementary measure for differentiating between malignant and benign lung lesions.

Cell Research, 2009

MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcri... more MicroRNAs are short regulatory RNAs that negatively modulate gene expression at the post-transcriptional level, and are deeply involved in the pathogenesis of several types of cancers. To investigate whether specific miRNAs and their target genes participate in the molecular pathogenesis of laryngeal carcinoma, oligonucleotide microarrays were used to assess the differential expression profiles of microRNAs and mRNAs in laryngeal carcinoma tissues compared with normal tissues. The oncogenic miRNA, microRNA-21 (miR-21), was found to be upregulated in laryngeal carcinoma tissues. Knockdown of miR-21 by specific antisense oligonucleotides inhibited the proliferation potential of HEp-2 cells, whereas overexpression of miR-21 elevated growth activity of the cells, as detected by the colony formation assay. The cell number reduction caused by miR-21 inhibition was due to the loss of control of the G1-S phase transition, instead of a noticeable increase in apoptosis. Subsequently, a new target gene of miR-21, BTG2, was found to be downregulated in laryngeal carcinoma tissues. BTG2 is known to act as a pan-cell cycle regulator and tumor suppressor. These findings indicate that aberrant expression of miR-21 may contribute to the malignant phenotype of laryngeal carcinoma by maintaining a low level of BTG2. The identification of the oncogenic miR-21 and its target gene, BTG2, in laryngeal carcinoma is potentially valuable for cancer diagnosis and therapy.

Personality and Individual Differences, 2013

ABSTRACT Individuals’ development is a multilayered affair. The influence of family relationship ... more ABSTRACT Individuals’ development is a multilayered affair. The influence of family relationship on personality, such as and focusing on birth order, is subject to influence from other social systems in which the families are situated. The current research examined the relation of birth order to personality and life satisfaction in China, where only children have become the majority because of national policy. Across two studies with both between-family data (N = 1468) and within-family data (N = 171), onlyborns and laterborns surpassed firstborns on openness to experience. In addition, only-child participants were more satisfied with their own lives than were sibling participants, especially laterborns. The results offer new insights into the dynamic relations between ecology and personality.

Learning and Individual Differences, 2013

Proceedings of the International Astronomical Union, 2010

How magnetic field structure changes with eruptive events (e.g., flares and CMEs) has been a long... more How magnetic field structure changes with eruptive events (e.g., flares and CMEs) has been a long-standing problem in solar physics. Here we present the analysis of eruptionassociated changes in the magnetic inclination angle, the transverse component of magnetic field and the Lorentz force. The analysis is based on an observation of the X3.4 flare on Dec.13 2006 and a numerical simulation of a solar eruption made by Yuhong Fan. Both observation and simulation show that (1) the magnetic inclination angle in the decayed peripheral penumbra increases, while that in the central area close to flaring polarity inversion line (PIL) deceases after the flare; (2) the transverse component of magnetic field increases at the lower altitude near flaring PIL after the flare. The result suggests that the field lines at flaring neutral line turn to more horizontal near the surface, that is in agreement with the prediction of Hudson, Fisher & Welsch (2008).

Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancem... more Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancement of inner penumbrae and central umbrae after major flares. In an effort to understand the physics behind the phenomena, we study the changes of magnetic inclination angle at the peripheral and the inner penumbral regions around the time of three X-class flares, the X3.4 flare on 2006 December 13, the X2.6 flare on 2005 January 15 and the X5.3 flare on 2001 August 25. For the first event, we use the Hinode Spectro-Polarimeter (SP) vector magnetograms before and after the flare, between which there was an 8-hour interval. For the two latter events, the high cadence vector magnetograms obtained with the Digital Vector Magnetograph (DVMG) at Big Bear Solar Observatory (BBSO) are available, with which we are able to study the inclination angle as a function of time. For all the events, we find that the mean inclination angle at the penumbral decay regions increases after flares. The result suggests that penumbral fields change from a more inclined to a more vertical configuration after the flare. Furthermore, we derive the three-dimensional coronal magnetic fields using nonlinear force-free field extrapolation to study the altitude variation of magnetic inclination angle.

Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancem... more Recent observations demonstrated the rapid penumbra decay in the outer δ-sunspot and the enhancement of inner penumbrae and central umbrae after major flares. In an effort to understand the physics behind the phenomena, we study the changes of magnetic inclination angle at the peripheral and the inner penumbral regions around the time of three X-class flares, the X3.4 flare on 2006 December 13, the X2.6 flare on 2005 January 15 and the X5.3 flare on 2001 August 25. For all the events, we find that the mean inclination angle at the penumbral decay regions increases after the flares. The result suggests that penumbral fields change from a more inclined to a more vertical configuration after the flare. Furthermore, we quantitatively compare our observations with recent MHD simulations of eruption, by Yuhong Fan which shows the evidence of field lines turn to more horizontal near the surface, immediately following the eruption.

Astrophysical Journal, 2011

It has been a long-standing question in solar physics how magnetic field structure changes with e... more It has been a long-standing question in solar physics how magnetic field structure changes with eruptive events (e.g., flares and coronal mass ejections). In this Letter, we present the eruption-associated changes in the magnetic inclination angle, the horizontal component of magnetic field vectors, and the Lorentz force. The analysis is based on the observation of the X3.4 flare on 2006 December 13 and in comparison to the numerical simulation of Fan. Both observation and simulation show that (1) the magnetic inclination angle in the decayed peripheral penumbra increases, while that in the central area close to the flaring polarity inversion line (PIL) deceases after the flare; (2) the horizontal component of magnetic field increases at the lower altitude near the flaring PIL after the flare. The result suggests that the field lines at the flaring neutral line turn to more horizontal near the surface, that is in agreement with the prediction of Hudson et al.

Astrophysical Journal, 2009

The Letter takes up a question of what radio emission is produced by electrons at the very accele... more The Letter takes up a question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that the radio emission from the acceleration sites: (i) has sufficiently strong intensity to be observed by currently available radio instruments and (ii) has spectra and light curves which are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.

New Astronomy, 2011

We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using m... more We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by , where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed.

The Astrophysical Journal, 2009

The Letter takes up a question of what radio emission is produced by electrons at the very accele... more The Letter takes up a question of what radio emission is produced by electrons at the very acceleration site of a solar flare. Specifically, we calculate incoherent radio emission produced within two competing acceleration models-stochastic acceleration by cascading MHD turbulence and regular acceleration in collapsing magnetic traps. Our analysis clearly demonstrates that the radio emission from the acceleration sites: (i) has sufficiently strong intensity to be observed by currently available radio instruments and (ii) has spectra and light curves which are distinctly different in these two competing models, which makes them observationally distinguishable. In particular, we suggest that some of the narrowband microwave and decimeter continuum bursts may be a signature of the stochastic acceleration in solar flares.

New Astronomy, 2011

We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using m... more We analyze in detail the X2.6 flare that occurred on 2005 January 15 in the NOAA AR 10720 using multiwavelength observations. There are several interesting properties of the flare that reveal possible two-stage magnetic reconnection similar to that in the physical picture of tether-cutting, where the magnetic fields of two separate loop systems reconnect at the flare core region, and subsequently a large flux rope forms, erupts, and breaks open the overlying arcade fields. The observed manifestations include: (1) remote Hα brightenings appear minutes before the main phase of the flare; (2) separation of the flare ribbons has a slow and a fast phase, and the flare hard X-ray emission appears in the later fast phase; (3) rapid transverse field enhancement near the magnetic polarity inversion line (PIL) is found to be associated with the flare. We conclude that the flare occurrence fits the tether-cutting reconnection picture in a special way, in which there are three flare ribbons outlining the sigmoid configuration. We also discuss this event in the context of what was predicted by , where the Lorentz force near the flaring PIL drops after the flare and consequently the magnetic field lines there turn to be more horizontal as we observed.

Science China-physics Mechanics & Astronomy, 2009

Recent studies showed a consistent pattern of changes in the sunspot structure associated with ma... more Recent studies showed a consistent pattern of changes in the sunspot structure associated with major flares: part of the peripheral penumbral regions vanishes during flares, and meanwhile, the umbral cores and/or inner penumbral regions are darkened. To understand the underlying physics of these observations, we compare the magnetic inclination angle in the decayed peripheral and the enhanced inner penumbral regions before and after the 4B/X3.4 flare of 2006 December 13 by using the high-resolution vector magnetograms from Hinode. We find that the mean inclination angle in the decayed penumbra increases after the flare while that in the enhanced penumbra near flaring neutral line decreases. The result confirms the previous idea that two components of a δ sunspot become connected after flares. As a result of new connection, peripheral penumbral fields change from a more inclined to a more vertical configuration and transverse fields in umbral core and inner penumbral regions increase substantially (Liu et al. 2005). The flare-associated changes of Doppler width as well as other parameters (the transverse field strength, continuum intensity and filling factor) are also presented.