The phrase "there exist challenges" is grammatically correct and can be used in written English.
It is typically used to introduce and acknowledge the existence of a problem or difficulty in a particular situation. Example: In the field of medicine, there exist challenges in providing affordable and accessible healthcare to rural communities.
Additive manufacture enables custom phantom manufacture, however there exist technical challenges, namely the lack of specialised materials to mimic radiation interaction properties of natural materials, and a lack of automated methods to reduce the manual effort required to convert medical scan data into an additive component.
Recently, Gao et al. have studied the maximum likelihood (ML) and the linear maximum SNR (LMSNR) channel estimation for two-way AF relay networks over the flat fading channels in [21], and pointed out that there exist many challenges since the channel estimation is required not only for data detection but also for self-cancelation at the two terminals.
Deletions finding on the HBV whole genome sequences is thus a very important issue though there exist underlying the challenges in mining such big and complex biological data.
Although it is meaningful to use fractional land cover for carbon simulation in large regions, there exists the challenge of correctly interpreting LUCC and its effects.
However, there exist significant challenges to be addressed for the realization of this objective.
However, there exist several challenges in assessing a map and comparing different maps.
Although there exist many challenges, such as establishing standards for microgrids design and construction, great R&D efforts have been made in the US, EU and around world.
Despite these efforts, there exist substantial challenges to achieving universal coverage of child immunization in developing countries, especially within the Sub Saharan African (SSA) region [31].
Despite the effectiveness of the MUSwiD and MUSwiDps user selection schemes in reducing the amount of feedback signaling from users to the relay, there exist some challenges that should be addressed before the multiuser switched diversity selection schemes can lend themselves for practical implementation.
