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\section{Scientific Justification}  Results from Herschel observations in far-infrared frequencies indicate a close relationship between the ubiquitous filamentary structures and the star formation. Numerical simulation and indirect evidence from Herschel observations suggest that stars form through gravitational fragmentation in filaments. This process is recently attested by a direct observation of fragmenting, gravitationally bound cores at an early stage, in B5 in the Perseus molecular cloud. L1689B serves as another relatively simple case of a young pre-stellar core sitting on a single filament, with a velocity gradient along the filament at parsec scales. We propose VLA observations of NH_3 (1, 1) and (2, 2) line emission of L1689B in order to trace the kinematics from the filament to the core, and \bf{thus {\bf thus  to examine the star forming process in the filament at an early stage}. \subsection{The case of B5 in the Perseus molecular cloud}  B5 in the Perseus molecular cloud was identified as a young pre-stellar core. Herschel observations shows that B5 sits in a filamentary strcutre, which extends for \~ 2 pc. FCRAO observations of ^{12}CO (1-0) and ^{13}CO (1-0) line emission show that the B5 region has a complicated velocity structure with multiple velocity components along the line of sight. Later with GBT observations of NH_3 (1, 1) and (2, 2) hyperfine lines, B5 is found to have a sub-sonic velocity structure, conforming to the theory of star formation in coherent cores. By combining the GBT and the VLA data of NH_3 hyperfine lines, Jaime et al. find fragmentation within the coherent core. This provides the first direct evidence of star formation through filament fragmentation.  Intriguingly, the projected morphology of the fragmented cores (with sizes of a few thousand AU) aligns well with the parsec-scale filament they sit in, as identified on the Herschel maps. This seems to suggest that the first stages of star forming process within filaments preserve the structure of the \it{mother {\it mother  filaments}. This is bizarre considering the difference in spatial scales of filaments (\~ a few parsec) and the condensations found by Jaime et al. (\~ a few thousand AU). To understand this phonomenon, it requires further analysis of the kinematics from the filament to the core and observations that are sensitive to the wide spatial scale range, of more young pre-stellar cores in filaments. \subsection{L1689B: Another B5 or a differenct case?}