The phrase "are difficult to further" is correct and usable in written English.
It can be used when discussing challenges in advancing or progressing a particular topic, idea, or situation.
Example: "The issues we are facing are difficult to further without additional resources or support."
Alternatives: "are hard to advance" or "are challenging to develop further".
However, as the dynamic characteristics of a practical passive mega-sub-controlled structure are very complicated, it is difficult to further all-sidedly examine the performance and the controlling effectiveness of this structure by a simple analytical model.
In addition, it was difficult to further degrade MB by increasing the irradiation time.
With the current data available, however, it was difficult to further constrain the H2O content in IBM magmas.
Since it is difficult to further constrain the value of ω, we refer to the most relaxed condition (ω = 3.8) in the following calculations.
Because NaBH4was used as the reduction agent, the synthesis process of the Au nanoparticles was fast and almost uncontrollable; it would be difficult to further improve the distribution by optimizing synthesis conditions.
The possible reason is that the electron transport from graphene to TiO2 (quantum tunneling) is difficult to further enhance by adding the RGO nanosheets because of their uncontrollable thickness (the tunneling probability of the photo-induced electrons dependent on the graphene thickness) [5].
Without additional experimental evidence, it is difficult to further evaluate the structural model for NaChBac.
However, it was difficult to further improve the lead from micromolar to even high nanomolar potency due to the unusually large enzyme-substrate interface of BoNTAe.
Unfortunately, given proprieties surrounding the Newbler software it is difficult to further interrogate the cause of the above results as the intricacies of this assembly algorithm are unknown.
Since Rs1-5HT1A chimeras with multiple internal domains replaced are not significantly expressed on the cell surface (data not shown), it may be difficult to further improve the potency of the Rs1.3 using our current approach.
