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1.
Proc Natl Acad Sci U S A ; 119(15): e2122793119, 2022 04 12.
Artigo em Inglês | MEDLINE | ID: mdl-35385356

RESUMO

Crystallography is the standard for determining the atomic structure of molecules. Unfortunately, many interesting molecules, including an extensive array of biological macromolecules, do not form crystals. While ultrashort and intense X-ray pulses from free-electron lasers are promising for imaging single isolated molecules with the so-called "diffraction before destruction" technique, nanocrystals are still needed for producing sufficient scattering signal for structure retrieval as implemented in serial femtosecond crystallography. Here, we show that a femtosecond laser pulse train may be used to align an ensemble of isolated molecules to a high level transiently, such that the diffraction pattern from the highly aligned molecules resembles that of a single molecule, allowing one to retrieve its atomic structure with a coherent diffraction imaging technique. In our experiment with CO2 molecules, a high degree of alignment is maintained for about 100 fs, and a precisely timed ultrashort relativistic electron beam from a table-top instrument is used to record the diffraction pattern within that duration. The diffraction pattern is further used to reconstruct the distribution of CO2 molecules with atomic resolution. Our results mark a significant step toward imaging noncrystallized molecules with atomic resolution and open opportunities in the study and control of dynamics in the molecular frame that provide information inaccessible with randomly oriented molecules.

2.
Nat Commun ; 13(1): 963, 2022 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-35181649

RESUMO

In low-dimensional systems with strong electronic correlations, the application of an ultrashort laser pulse often yields novel phases that are otherwise inaccessible. The central challenge in understanding such phenomena is to determine how dimensionality and many-body correlations together govern the pathway of a non-adiabatic transition. To this end, we examine a layered compound, 1T-TiSe2, whose three-dimensional charge-density-wave (3D CDW) state also features exciton condensation due to strong electron-hole interactions. We find that photoexcitation suppresses the equilibrium 3D CDW while creating a nonequilibrium 2D CDW. Remarkably, the dimension reduction does not occur unless bound electron-hole pairs are broken. This relation suggests that excitonic correlations maintain the out-of-plane CDW coherence, settling a long-standing debate over their role in the CDW transition. Our findings demonstrate how optical manipulation of electronic interaction enables one to control the dimensionality of a broken-symmetry order, paving the way for realizing other emergent states in strongly correlated systems.

3.
Nature ; 595(7866): 239-244, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-34234338

RESUMO

Exotic phenomena can be achieved in quantum materials by confining electronic states into two dimensions. For example, relativistic fermions are realized in a single layer of carbon atoms1, the quantized Hall effect can result from two-dimensional (2D) systems2,3, and the superconducting transition temperature can be considerably increased in a one-atomic-layer material4,5. Ordinarily, a 2D electronic system can be obtained by exfoliating the layered materials, growing monolayer materials on substrates, or establishing interfaces between different materials. Here we use femtosecond infrared laser pulses to invert the periodic lattice distortion sectionally in a three-dimensional (3D) charge density wave material (1T-TiSe2), creating macroscopic domain walls of transient 2D ordered electronic states with unusual properties. The corresponding ultrafast electronic and lattice dynamics are captured by time-resolved and angle-resolved photoemission spectroscopy6 and ultrafast electron diffraction at energies of the order of megaelectronvolts7. Moreover, in the photoinduced 2D domain wall near the surface we identify a phase with enhanced density of states and signatures of potential opening of an energy gap near the Fermi energy. Such optical modulation of atomic motion is an alternative path towards realizing 2D electronic states and will be a useful platform upon which novel phases in quantum materials may be discovered.

4.
Phys Rev Lett ; 124(13): 134803, 2020 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-32302182

RESUMO

We propose and demonstrate a novel scheme to produce ultrashort and ultrastable MeV electron beam. In this scheme, the electron beam produced in a photocathode radio frequency (rf) gun first expands under its own Coulomb force with which a positive energy chirp is imprinted in the beam longitudinal phase space. The beam is then sent through a double bend achromat with positive longitudinal dispersion where electrons at the bunch tail with lower energies follow shorter paths and thus catch up with the bunch head, leading to longitudinal bunch compression. We show that with optimized parameter sets, the whole beam path from the electron source to the compression point can be made isochronous such that the time of flight for the electron beam is immune to the fluctuations of rf amplitude. With a laser-driven THz deflector, the bunch length and arrival time jitter for a 20 fC beam after bunch compression are measured to be about 29 fs (FWHM) and 22 fs (FWHM), respectively. Such an ultrashort and ultrastable electron beam allows us to achieve 50 femtosecond (FWHM) resolution in MeV ultrafast electron diffraction where lattice oscillation at 2.6 THz corresponding to Bismuth A_{1g} mode is clearly observed without correcting both the short-term timing jitter and long-term timing drift. Furthermore, oscillating weak diffuse scattering signal related to phonon coupling and decay is also clearly resolved thanks to the improved temporal resolution and increased electron flux. We expect that this technique will have a strong impact in emerging ultrashort electron beam based facilities and applications.

5.
Zhonghua Yi Xue Yi Chuan Xue Za Zhi ; 37(4): 459-461, 2020 Apr 10.
Artigo em Chinês | MEDLINE | ID: mdl-32219837

RESUMO

OBJECTIVE: To explore the genetic basis for a child featuring delayed intellectual development. METHODS: The child and his parents were subjected to conventional G-banding karyotyping and single nucleotide polymorphism array (SNP-array) analysis. Suspected copy number variations (CNVs) were verified in both parents. RESULTS: No karyotypic abnormality was found with the child and his parents. SNP-array results for both parents were normal. The child was found to harbor a de novo 172 kb deletion at 18q21.2 with a physical position of 52 957 042-53 129 237. The deletion only involved one OMIM gene, namely TCF4, resulting in removal of its exons 6 to 8. CONCLUSION: The SNP-array assay has facilitated with the diagnosis of this child. Deletion of 18q21.2 region probably accounts for the Pitt-Hopkins syndrome (PTHS) in this patient.


Assuntos
Variações do Número de Cópias de DNA , Hiperventilação/genética , Deficiência Intelectual/genética , Fator de Transcrição 4/genética , Criança , Deleção Cromossômica , Cromossomos Humanos Par 18/genética , Deficiências do Desenvolvimento/genética , Facies , Humanos , Fenótipo
6.
Zhonghua Yi Xue Yi Chuan Xue Za Zhi ; 37(2): 131-134, 2020 Feb 10.
Artigo em Chinês | MEDLINE | ID: mdl-32034737

RESUMO

OBJECTIVE: To explore the genetic basis for a child featuring severe mental retardation. METHODS: The child was subjected to target region capture and next generation sequencing. Suspected variants were verified by Sanger sequencing. RESULTS: The child was found to harbor a hemizygous c.1A>G (pMet1?) variation of the ARX gene, for which his mother was a heterozygous carrier. The mutation was unreported previously and was predicted to be "probably pathogenic" by bioinformatic analysis. CONCLUSION: The c.1A>G (pMet1?) variant of the ARX gene may underlie the occurrence of severe mental retardation in this child.


Assuntos
Deficiência Intelectual , Criança , Códon , Heterozigoto , Sequenciamento de Nucleotídeos em Larga Escala , Proteínas de Homeodomínio , Humanos , Deficiência Intelectual/genética , Mutação , Fatores de Transcrição
7.
Zhonghua Yi Xue Yi Chuan Xue Za Zhi ; 36(11): 1111-1114, 2019 Nov 10.
Artigo em Chinês | MEDLINE | ID: mdl-31703138

RESUMO

OBJECTIVE: To explore the clinical features and molecular basis for a child featuring infantile epilepsy and developmental disorders. METHODS: Clinical data and peripheral blood samples of the child and his parents were collected. The coding regions of genes associated with nervous system development were subjected to target region capture sequencing. RESULTS: The child developed generalized spasm at 3 months and was diagnosed with epilepsy at 6 months of age. He was treated with Depakin but was diagnosed with mental retardation and developmental retardation at 3 years of age. A novel heterozygous c.3842T to G variant of the SYNE1 gene was detected. His father was found to carry the same variant and had a history of convulsions in infancy but with no mental or developmental anomalies. CONCLUSION: A novel variant of SYNE1 gene was identified in this child, and the prognosis may be poor.


Assuntos
Deficiências do Desenvolvimento/genética , Epilepsia/genética , Proteínas do Tecido Nervoso/genética , Proteínas Nucleares/genética , Pré-Escolar , Proteínas do Citoesqueleto , Deficiências do Desenvolvimento/complicações , Epilepsia/complicações , Humanos , Lactente , Deficiência Intelectual/complicações , Deficiência Intelectual/genética , Masculino , Mutação , Convulsões
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